Human choice behavior was assessed in a concurrent-chains schedule, where two equal initial links (IL) each led to a distinct terminal-link (TL). One TL was associated with a fixed ratio schedule of reinforcement, while the other was associated with a bi-valued mixed ratio schedule of reinforcement, whose arithmetic mean equaled the Fixed TL schedule. The fixed component (FR50; FR25; FR5) was arranged to be equal to the alternative mixed component in each condition (FR1/99; FR1/49; FR1/9), and choice behavior was measured by proportion of responses to each IL. In addition, the IL duration varied across conditions (VI 30s; VI 15s; FI 1s). Preference for the mixed option was observed with longer durations (e.g. when IL = VI 30s and TL = FR1/99). Participants were relatively indifferent in other conditions, though the results suggested a monotonic increase in preference as either durations or programmed efforts increased. It is concluded that both choice and the conditioned reinforcement value of the mixed option are contextually based, so that the value of a stimulus correlated with an immediate reward (i.e. FR 1) is enhanced the greater the temporal context in which the FR1 is embedded.

Thick platinum coatings on glass microspheres are needed for proposed Laser Fusion targets. The spherical nature of these substrates coupled with the small dimensions (M.00 ym OD) make it difficult to achieve a smooth and uniform coating. Coating problems encountered include a rough surface and porous microstructure from the oblique incidence and lack of temperature and bias control, "clumping" of the microspheres causing non-uniformities, and particle accumulation causing "cone" defects.Sputtering parameters significantly affecting the coatings include total pressure, DC substrate bias, and the addition of doping gases. Using an ultrasonic vibrating screened cage and RF magnetron Sputtergun, we have successfully batch coated microspheres with up to 6 um of Pt, with a surface roughness of 200 nm, thickness non-concentricity of 300 nm, and density greater than 98% of bulk Pt.

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Self-control was studied in an iterated one-player Prisoner's Dilemma game in which students' choices affected the payoff matrix on the next trial. The frequency of selfcontrol responses (choice of the smaller payoff now, but with the more generous payoff matrix more likely on the next trial) and defection responses (choice of the larger payoff now, but with the less generous payoff matrix more likely on the next trial) were measured. In Experiment 1, players achieved a criterion of five consecutive self-control responses more quickly as a positive function of trial spacing, the presence between trials of a discriminative stimulus associated with the upcoming payoff matrix, and the probability that the self-control or defection response would be reciprocated by the computer. Experiment 2 replicated the effect of trial spacing except when there was an interfering task during the interval, suggesting that trial spacing permits better appreciation of the contingencies.

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