Flows in lung bifurcations are complicated by geometry, and it is recognized that accurate lung dosimetric models require realistic calculations of the flow and particle deposition patterns. A computational fluid dynamics study of flow and particle concentration has been carried out for a lung bifurcation based on the model developed by Weibel. The predicted flow patterns match well with previously reported experimental data. Secondary flow patterns and locations close to the walls having high particle concentrations are clearly seen.
A selection of experimental viscosity and slip measurements are reported for He and Ar. The measured values have been made with a modified spinning rotor gauge (SRG-2; MKS Instruments, Inc.) where the sphere is coaxially rotated in the cylindrical tube housing. All of the experiments were conducted in the slip regime in accordance with the theory previously developed [S. K. Loyalka, J. Vac. Sci. Technol. A 14, 2940 (1996)]. The theoretical results from this previous article allow one to extract values of the viscosity, the velocity slip coefficient, and the tangential momentum accommodation coefficient from the experimentally obtained angular retardation data for each gas without a need for calibration of the system against a known gas viscosity. Since the existing manufactured SRGs mount horizontally with the rotor angular momentum vector oriented vertically, the required SRG modifications were necessarily limited to the interior of the mounting tube. Here, an insert was developed for the mounting tube in which was bored a short, vertically oriented, cylindrical hole in which the rotor could turn coaxially. Measurements made with this modified version of the SRG are compared with previous experimental results and a discussion of the errors associated with both wall and end effects is included.
The use of a photon intermediate direct energy conversion (PIDEC) process to develop a proof of concept of a long-lived and efficient nuclear battery powered by a radioactive beta source is discussed. Fundamentally, PIDEC is a means of matching the scale length of the range of radiation to the scale length of the transducer. The device uses a photovoltaic cell and excimer gas-based photon source. In this work, argon was used to produce the excimer photon source (argon excimer at 129 nm) with a pressure range from 7 × 10-3 to 1.4 × 107 Pa (10-6 to 2100 psig). The beta source used in this study was a 90Sr source that has a daughter, 90Y, that then decays to stable 90Zr. Intermediate shielding from lead and an argon gas plenum were used to prevent damage to the photovoltaic cell. This battery demonstrated power variations with gas pressure as expected, and no radiation damage to the photovoltaic cell was observed over a period in excess of 150 h. Such a long exposure period demonstrates the desired tolerance of the device to the direct radiation damage that would otherwise be sustained in normal semiconductor-based energy conversion systems.
