This paper describes how damage propagation can be modeled within the modules of aircraft gas turbine engines. To that end, response surfaces of all sensors are generated via a thermo-dynamical simulation model for the engine as a function of variations of flow and efficiency of the modules of interest. An exponential rate of change for flow and efficiency loss was imposed for each data set, starting at a randomly chosen initial deterioration set point. The rate of change of the flow and efficiency denotes an otherwise unspecified fault with increasingly worsening effect. The rates of change of the faults were constrained to an upper threshold but were otherwise chosen randomly. Damage propagation was allowed to continue until a failure criterion was reached. A health index was defined as the minimum of several superimposed operational margins at any given time instant and the failure criterion is reached when health index reaches zero. Output of the model was the time series (cycles) of sensed measurements typically available from aircraft gas turbine engines. The data generated were used as challenge data for the Prognostics and Health Management (PHM) data competition atPHM'08.

Lighting has been shown to be an effective tool in the fight against crime, but too often the tool has been a sledgehammer. The four field studies described in this paper set out to answer two questions: 'How much light is needed to provide a perception of safety at night in urban and suburban areas?' and 'How important is light spectrum to that tion?' The first two field studies examined people's perceptions of the quality of the lighting for security on streets in New York City and Albany, New York. The third measured people's perceptions of safety when walking alone in urban and suburban parking lots, by day and night. The fourth measured perceptions of safety in a parking lot lit by high-pressure sodium and metal halide lamps. Taken together, these studies indicate that an average horizontal illuminance on a parking lot surface or street sidewalk of about 30 Ix provides enough light to ensure that perceptions of safety are close to what they are in daylight. The light spectrum is a minor factor relative to illuminance.

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