Proton elastic scattering angular distributions were measured for 12 C, 27 A1, 40 Ca, 58 Ni, 68 Zn, 90 Zr, 116 Sn, and 208 Pb with a 61.4-MeV beam from the Oak Ridge isochronous cyclotron. An optical-model analysis of the data was performed. The results show a nuclear symmetry dependence of the optical-model potential; this dependence can be related to either the real well depth or the radius parameter of the real well. This study, combined with previously reported studies at lower bombarding energies, shows that for targets of ^4>27 a potential with fixed-geometry parameters and an energy-dependent real well depth, -{V-OAZ/A 11 *) «[49.9-0.215£+26.0(iV--£)A4] MeV, will predict angular distributions in reasonable agreement with experiment for bombarding energies of 30-61 MeV. Data from light targets show a preference for large volume absorption and small surface absorption terms in the potential, while heavy-target data show a preference for small volume absorption and large surface absorption terms. The mean free path for a reaction of a 61-MeV proton in nuclear matter is estimated to be about 7J F.

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It has been argued that the control of instrumental action by motivational states is indirect, being mediated by the effects these states have on the incentive value of the instrumental outcome (A. Dickinson & B. W. Balleine, 1994). In this study, the benzodiazepine agonist midazolam was found to control instrumental action in a similar manner. Midazolam (1 mg/kg) increased rewarded instrumental performance in rats trained undeprived but only elevated performance in extinction when rats were reexposed to the instrumental outcome under midazolam before the test. This effect of reexposure under midazolam did not transfer to a test conducted under food deprivation, suggesting that it was not produced by drug-induced hunger. Finally, in animals trained hungry, midazolam was found to block outcome devaluation induced by a reduction in food deprivation, indicating that midazolam and food deprivation affect outcome value via a common substrate.