An electrical network model for computing current distribution in a spirally wound lithium ion cell

Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2012."September 2012." Page 74 blank. Cataloged from PDF version of thesis.Includes bibliographical references.Lithium ion batteries are the most viable option for electric vehicles but they still have significant limitations. Safety of these batteries is one of the concerns that need to be addressed when they are used in mainstream vehicles, because of heating issues that may lead to thermal runaway. This work aims at supplementing the existing electrochemical heat distribution model of a spirally wound lithium ion battery with an electrical network that can model the heat losses due to electric resistances of the current collectors. The developed electrical network model is used to calculate the current and state-of-charge distribution throughout the spiral jelly roll, which can be used to determine electric heat losses. The results obtained from this model can then be used to optimize the shape and dimensions of the current collectors as well as the materials used in them.by Somani Patnaik.M. Eng

Evaluating the accuracy of data collection on mobile phones: A study of forms, SMS, and voice

While mobile phones have found broad application in reporting health, financial, and environmental data, there has been little study of the possible errors incurred during mobile data collection. This paper provides the first (to our knowledge) quantitative evaluation of data entry accuracy on mobile phones in a resource-poor setting. Via a study of 13 users in Gujarat, India, we evaluated three user interfaces: 1) electronic forms, containing numeric fields and multiple-choice menus, 2) SMS, where users enter delimited text messages according to printed cue cards, and 3) voice, where users call an operator and dictate the data in real-time. Our results indicate error rates (per datum entered) of 4.2% for electronic forms, 4.8% for SMS, and 0.45% for voice. These results caused us to migrate our own initiative (a tuberculosis treatment program in rural India) from electronic forms to voice, in order to avoid errors on critical health data. While our study has some limitations, including varied backgrounds and training of participants, it suggests that some care is needed in deploying electronic interfaces in resource-poor settings. Further, it raises the possibility of using voice as a low-tech, high-accuracy, and cost-effective interface for mobile data collection.Massachusetts Institute of Technology. Public Service Cente