A method of programming a memory cell in a non-volatile memory device includes applying a first voltage to a control gate associated with the memory cell and applying a second voltage to a drain region associated with the memory cell. A Viterbi algorithm is applied to the observation vectors given the parameters of a hierarchical statistical model for each object, and a face is identified by finding a highest matching score between an observation sequence and the hierarchical statistical model. a graphical user interface that facilitates insight discovery and exploration of product affinities across time, generated by a purchase sequence analysis of a retailer’s transaction data. The sensing device may be configured to transmit gas detection information to an external wireless communication device, and the wireless communication device may be configured to generate an alert if a gas concentration level rises above a predetermined acceptable level.