Volunteering a Public Service: An Experimental Investigation

In some public goods environments it may be advantageous for heterogeneous groups to be coordinated by a single individual. This “volunteer” will bear private costs for acting as the leader while enabling each member of the group to achieve maximum potential gains. This environment is modeled as a War of Attrition game in which everyone can wait for someone else to volunteer. Since these games generally have multiple Nash equilibria but a unique subgameperfect equilibrium, we tested experimentally the predictive power of the subgame-perfection criterion. Our data contradict that subjects saw the subgame-perfect strategy combination as the obvious way to play the game. An alternative behavioral hypothesis – that subjects were unable to predict accurately how their opponents would play and tried to maximize their expected payoff – is proposed. This hypothesis fits the observed data generally well.

Can shared surfaces be safely negotiated by blind and partially sighted people?

‘Shared Space’ schemes are designed to remove the physical distinction between pedestrian space and traffic space in the street environment to encourage more pedestrians to use the area. They may also make it easier for people with wheelchairs, prams or similar to negotiate the space. However, by removing the kerbs, blind and partially sighted people lose one of the key references that they normally use to know they are in a safe space away from vehicles and to navigate around the area. This study is intended to understand what people with visual impairments need from a surface to make it clearly detectable, given that it should not be a barrier to progress for people with other mobility limitations. With this information, some surfaces were tested to determine their suitability as a delineator. Approach and/or Methodology An experimental approach was adopted. People with mobility impairments and blind and partially sighted people were recruited. All participants used the normal street environment unaccompanied. The blind and partially sighted participants included people who use a guide dog, those who use a long cane and those who use no assistive device. The people with mobility impairments all used some form of mobility aid for example walking stick or wheelchair. The tests were run in the pedestrian testing facility PAMELA at UCL. The top surface of the test facility was predominantly concrete paving slab, but with test surfaces discretely located. The task for all participants was to travel from one designated place in the test area to another. For some of these trials the participant would encounter one of the test surfaces, but on other trials they would not. After each trial the participants were asked to rate how easy it was to detect a change in surface, or how easy it was to pass over the surface. The different surfaces included blister paving, corduroy paving, a central delineator, slopes, roughened surfaces, and traditional kerb upstands of different heights. Results or Expected Results None of the 400mm wide surfaces was detected by all participants. Changes in level through slopes were considered both positively and negatively, some people asking for steeper gradients and some less steep. Kerb heights below 60mm were not reliably detectable by blind or partially sighted people and are an obstacle to people in wheelchairs. Further tests on more surfaces are in process and the results will be incorporated into this paper. Conclusion Early suggestions for detectable surfaces – proposed in UK schemes - have been either a barrier to people with mobility impairments, or difficult to detect for blind and partially sighted people or both. The work presented in this paper shows the difficulty in finding a suitable dual purpose surface, yet clarifies the design requirements for shared space delineators for people with mobility impairments and blind or partially sighted people. This work has reinforced the point that 400mm width is insufficient to be used as a tactile surface. Further conclusions will be made after the additional surface tests. Topic Code: Ca C. Accessibility concerns and solutions for those with cognitive and sensory impairment a. Pedestrian safety at crossings and intersection

Vibration characteristics of the HPOTP (High Pressure Oxygen Turbopump) of the SSME (Space Shuttle Main Engine)

A review is presented of various rotordynamic problems which have been encountered and eliminated in developing the current flight engines, and continuing subsynchronous problems which are being encountered in developing a 109% power level engine. The basic model for the High Pressure Oxygen Turbopump (HPOTP) of the SSME including the structural dynamic model for the rotor and housing and component models for the liquid and gas seals, turbine-clearance excitation forces, and impeller-diffuser forces are discussed. Results from a linear model are used to examine the synchronous response and stability characteristics of the HPOTP, examining bearing load and stability problems associated with the second critical speed. Various seal modifications are examined and shown to have favorable consequences with respect to bearing reactions and stability