Atomistic simulations of Ga atom ordering in Pu 5?at. % Ga alloys

We employ molecular dynamics and Monte Carlo (MC) methods to simulate the rearrangement of Ga atoms from a randomly distributed Pu-Ga alloy and study the resultant effect on thermodynamic properties. The results show that all of the first neighbor Ga-Ga bonds are removed at all temperatures considered (200, 400 and 600 K) while the number of 2NN and 3NN bonds increase, and the number of 4NN bonds decreases. These results imply that Ga atoms develop strong short range ordering in the solid solution. The ordering causes an enthalpy decrease about ~3–4 meV/atom for different temperatures in the 5 at. % Ga alloy. This energy change is clearly important in the calculation of the Pu-Ga phase diagram. In addition, MC calculations at 200 K show pronounced Ga segregation.     

Using the modified embedded-atom method to calculate the properties of Pu-Ga alloys

In this article, the semi-empirical modified embedded atom method is used to develop a model of Pu-Ga alloys. Employing classical calculations, the model is used to predict thermodynamic properties of these alloys as well as the complex Pu-Ga phase diagram. For more information contact M.I. Baskes, Los Alamos National Laboratory, P.O. Box 1663, MS-G755, Los Alamos, NM 87545, USA; (505) 667-1238; fax (505) 667-8021; baskes@lanl.gov.     

Morphine taste conditioning and analgesia: Assessing conditioned and novelty-induced analgesia.

In previous work showing a taste-elicited decrease in pain sensitivity (J. S. Miller, K. S. Kelly, J. L. Neisewander, D. F. McCoy, & M. T. Bardo, 1990), the rats (Rattus norvegicus) were always habituated to an inactive hot plate after each drug injection. The present report examined whether the analgesic response was a conditioned response to the taste or a response to the novelty of the hot plate resulting from morphine disrupting the habituation process. In 3 experiments, it was found that hot plate novelty was mainly responsible for the analgesic response. For example, increasing the number of conditioning trials did not enhance analgesia in morphine-treated rats. Rather, it attenuated analgesia in saline-treated controls (habituation). Also, rats given habituation in a drug-free state failed to show an analgesic response compared with controls. (PsycINFO Database Record (c) 2010 APA, all rights reserved)