Exploration of the transition from the hydrodynamiclike to the strongly kinetic regime in shock-driven implosions.

Clear evidence of the transition from hydrodynamiclike to strongly kinetic shock-driven implosions is, for the first time, revealed and quantitatively assessed. Implosions with a range of initial equimolar D3He gas densities show that as the density is decreased, hydrodynamic simulations strongly diverge from and increasingly overpredict the observed nuclear yields, from a factor of ∼2 at 3.1 mg/cm3 to a factor of 100 at 0.14 mg/cm3. (The corresponding Knudsen number, the ratio of ion mean-free path to minimum shell radius, varied from 0.3 to 9; similarly, the ratio of fusion burn duration to ion diffusion time, another figure of merit of kinetic effects, varied from 0.3 to 14.) This result is shown to be unrelated to the effects of hydrodynamic mix. As a first step to garner insight into this transition, a reduced ion kinetic (RIK) model that includes gradient-diffusion and loss-term approximations to several transport processes was implemented within the framework of a one-dimensional radiation-transport code. After empirical calibration, the RIK simulations reproduce the observed yield trends, largely as a result of ion diffusion and the depletion of the reacting tail ions.

Data quality in a distributed data processing system: the SHEP Pilot Study.

The Systolic Hypertension in the Elderly Program (SHEP) Pilot was a collaborative clinical trial that distributed to the clinics all data processing tasks except for randomization assignment codes and morbidity and mortality data. The clinics used customized programs to enter and verify data interactively, to maintain their own local master files, and to transmit the data electronically to the Coordinating Center. We measured quality control based on criteria from centralized as well as distributed models: the error rate for baseline forms was 0.5 per 1000 items. Ninety-eight percent of the forms were query-free, and a central reentry of the data in a 5% sample yielded a miskey rate of 2 per 1000 items. The potential problems of distributed data processing are vulnerability of the local master files and the time demands on Coordinating Center programmers for maintaining clinic computer systems. The advantages are the active involvement of clinic staff in their own quality control, the functional accessibility of the clinics to the Coordinating Center in controlling protocol decisions and data monitoring, and the level of accuracy, completeness, and timeliness of the data that can be achieved.