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Renewable energy technologies have been actively pursued in order to meet increasing energy demand and mitigating environmental pollution. Proton exchange membrane fuel cell (PEMFC) is a promising technology with a high energy conversion efficiency to replace the traditional internal combustion engine in automobiles while producing no greenhouse emission. However, the high cost of Pt based electrocatalysts for promoting oxygen reduction reaction (ORR) at the cathode hampers the widespread application of PEMFCs. Showing encouraging performance, non-precious transition metal and nitrogen co-doped carbon electrocatalysts have been extensively developed as cost-effective ORR catalysts in PEMFCs. This research aims to predict the chemical nature of active sites, kinetic activity for ORR, and structural stability in electrochemical conditions of Mn and N co-doped carbon (denoted as Mn-N-C) catalyst using the first principles density functional theory (DFT) methods. Both D1 type MnN4 (i.e., a Mn atom coordinated with four pyrrolic N) and D2 type MnN4 (i.e., a Mn atom coordinated with four pyridinic N) moieties embedded in a carbon graphene layer have been predicted to be active for four-electron ORR in acid media, explaining well available experimental measurement results. Notably, the D1 site was predicted to have a superior limiting potential of 0.80 V for ORR, as compared to the value of 0.54 V on the D2 site, indicating a higher intrinsic ORR activity on the D1 sites. By contrast, the D2 site has been predicted to exhibit enhanced electrochemical stability over the D1 site, as evidenced by the predictions that the free energy change for demetallation process is 0.36 eV higher for the D2 site than the D1 site. Moreover, a constant potential computational method combined with a microkinetic model for ORR has been developed and applied to predict the half-wave potential of ORR to be 0.73 V on D2 site, agreeing well with experimental values to validate the developed computational approach. Motivated by the predicted stability of two types of MnN4 sites, the free energy evolution along a transformation pathway from D1 to D2 site has been computed to examine novel synthesis concept for enhancing the electrochemical stability of Mn-N-C catalysts.

Image-based dietary assessment is important for health monitoring and obesity management because it can provides quantitative food intake information. In this thesis, a novel image processing method that estimates the volume of food within a circular bowl (i.e., the top rim of the bowl is a circle) is presented. In contrast to the Western culture where circular plates are most commonly used as food containers, circular bowls are the primary food containers in Asian and African culture. This thesis focuses on estimating the volume of amorphous food (i.e., food without a clear shape, such as a bowl of cereal) instead of food with usual shapes (e.g., an apple). Four geometric features of the food, namely food orientation, food area ratio, normalized curvature and normalized shape vertex, are extracted from 2D images. Based on these features, food volume is estimated using a linear or quadratic regression model. Our experiments show that, for 135 images of six different foods in a bowl of known shape, the mean absolute percentage error of our estimation was less than 20\%, evaluated using a five-fold cross-validation technique.

Private data querying (PDQ) is about querying a database held by a server without: i) revealing any information about the query to the server, and ii) learning more information than the result of the query. Prior solutions to the PDQ problem require linear (in the size of the dataset) computation and communication, which is impractical for large datasets. In this thesis, we propose a new model for secure computation that separates PDQ protocols into two phases: a precomputation phase and a query phase. We introduce a scheme with sublinear computation and communication query cost under the assumption that the data owner can do a reasonable amount of computation at the precomputation phase. This assumption is reasonable in many environments when the data is known ahead of time and the queries are known at a later time. We also introduce such protocols for the following database problems: existence problem, message lookup, the rank of query, one dimensional query, two dimensional range query, a small data change by the server.