A combination thermodynamic perturbation and umbrella sampling study predicts two free energy wells for the rotational isomerization of the variant-3 scorpion neurotoxin tryptophan-47 indole side chain. One well has the indole side chain in the crystallographic orientation; the other has the indole rotated approximately 220 degrees to form a new conformation with a relative free energy of 3 +/- 2 kcal/mol. The activation barrier is 8.5 kcal/mol from the crystallographic well, from which transition state theory predicts a rate of escape of 2 x 10(5) s-1. Correlations in the displacements of side chains neighboring tryptophan-47 and the isomerization reaction coordinate last up to 20 ps. Favorable conditions of experimental verification are discussed.
The services received by a process from a time-sharing operating system can be characterized by a resource count ~ wiRij where Ri~ is the number of units of service received by process j from resource i and wl is the cost per unit of the service. Each class of users can be characterized by a policy function which specifies the amount of service a user who belongs to this class should receive as a function of time. Priority changes dynamically as a function of the difference between the service promised to the user by the policy function and the service he actually receives.A scheduling and swapping algorithm which keeps the resource count of each process above its policy function will provide the specified level of service. Overhead can be reduced by avoiding swaps of processes which have received at least this level of service. The algorithm has been implemented in a general purpose operating system, and it has provided significantly better service to interactive and to batch jobs than the previous scheduler.KEY WORDS AND PHRASES: scheduler, time-sharlng, operating resource allocation and swapping CR CATEGORIES: 4.32 system,
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