A Non-Equilibrium Molecular Dynamics Study of the Effects of Helium Bubbles on the Thermal Conductivity of ZrC

Zirconium carbide (ZrC) has been proposed as a potential improvement to nuclear fuel cladding. As such, it is important to characterize its physical properties, particularly those relating to thermal energy transport. Reactor conditions are known to damage fuel microstructure over time. While research has been conducted on undamaged and damaged ZrC, some areas of interest remain. Fission products, such as helium, can accumulate in pores within the fuel microstructure. Such a case has yet to be characterized in ZrC fuel cladding. A non-equilibrium molecular dynamics model was developed to characterize the thermal properties of ZrC. Fourier’s Law allows the thermal conductivity of ZrC to be determined based on the relationship between heat flux and temperature gradient. The thermal conductivity of an undamaged ZrC lattice is compared to the thermal conductivity of a damaged lattice. The values of thermal conductivity demonstrating the impact of damage from pores and helium-filled pores are reported

Pegasus: A Geosynchronous Launch Profile

Pegasus is a low cost system which can carry a 600 pound payload to 250 nautical mile polar orbits as well as larger payloads to lower altitude/ lower inclination orbits or suborbital trajectories. The craft is carried aloft by a conventional transport/bomber-class aircraft and launched from level flight at approximately 40,000 ft. The first flight of Pegasus was made on April 5, 1990 over the Western Test Range at an altitude of 43,000 feet using the NASA B-52. The unmanned launch vehicle was developed jointly by Orbital Science Corporation (OSC) and Hercules Aerospace Company and the first flight which reached a 320 nmi orbit was conducted by, DARPA (Defense Advanced Research Projects Agency) and NASA\u27s Goddard Space Flight Center. The Pegasus launcher is 49.2 feet in length, has a diameter of 50 inches and a gross weight of 41,000 pounds. The payload can have a length up to 72 inches and a diameter of 46 inches. A 3-axis, gravity gradient or spin-stabilized spacecraft can be achieved or a number of small satellites can be inserted. A preliminary propulsion design analysis for the launching of a small geosynchronous Earth satellite aboard Pegasus was performed. The problem for the positioning of the satellite is presented with emphasis on the effects of orbital parameters such as the Low-Earth Orbit (LEO) altitude, propellant, and launch site latitude on the spacecraft\u27s propellant budget and beginning of life (BOL) mass. A comparison of conventional launch vehicles and the Pegasus launch vehicle is also presented. A Pegasus fourth stage was sized based on the propellant mass required for geosynchronous orbit (GEO) injection. Recommendations for a launch profile were made based upon minimizing the propellant used in the apogee boost motor (ABM) and perigee boost motor (PBH) or fourth stage used to place a small satellite into geosynchronous orbit

Ends, Means and Utility Functions: The Efficiency Criterion and Enforcement Activity in Canadian Antitrust 1970-1981

The object of this paper is twofold: to determine the extent to which enforcement of the Combines Investigation Act from 1970-1981 was guided by the goal of maximizing economic efficiency; and to ascertain the roles - facilitating or frustrating - played by the government and the Bureau of Competition Policy. The former is accomplished by correlating Bureau enforcement activity with estimates of allocative inefficiency. The latter is accomplished by treating the Bureau as a utility maximizer subject to the constraints imposed by the legislation and the structures set up to administer and adjudicate the statute. Our conclusions are that: enforcement activity is not guided by efficiency considerations; and the chief reason is the government constraints, particularly the wording of the legislation and its implicit support of the economic analysis of the courts

Directional characteristics of lunar thermal emission

Directional characteristics and brightness temperatures of thermal lunar emissio

Apollo experiment S-217 IR/radar study of Apollo data

An experiment using Earth based remote sensing radar, infrared eclipse, and color difference data to deduce surface properties not visible in Apollo photography is reported. The Earth based data provided information on the small scale (centimeter sized) blockiness and on the surface chemical composition (titanium and iron contents) of the lunar surface. These deduced surface properties complemented the new Apollo photography, leading to refined geologic interpretations of the lunar surface

Surface materials of the Viking landing sites

Martian surface materials viewed by the two Viking landers (VL-1 and VL-2) range from fine-grained nearly cohesionless soils to rocks. Footpad 2 of VL-1, which landed at 2.30 m/s, penetrated 16.5 cm into very fine grained dunelike drift material; footpad 3 rests on a rocky soil which it penetrated ≈3.6 cm. Further penetration by footpad 2 may have been arrested by a hard substrate. Penetration by footpad 3 is less than would be expected for a typical lunar regolith. During landing, retroengine exhausts eroded the surface and propelled grains and rocks which produced craters on impact with the surface. Trenches excavated in drift material by the sampler have steep walls with up to 6 cm of relief. Incipient failure of the walls and failures at the end of the trenches are compatible with a cohesion near 10–10^2 N/m^2. Trenching in rocky soil excavated clods and possibly rocks. In two of five samples, commanded sampler extensions were not achieved, a situation indicating that buried rocks or local areas with large cohesions (≥10 kN/m^2) or both are present. Footpad 2 of VL-2, which landed at a velocity between 1.95 and 2.34 m/s, is partly on a rock, and footpad 3 appears to have struck one; penetration and leg strokes are small. Retroengine exhausts produced more erosion than occurred for VL-1 owing to increased thrust levels just before touchdown. Deformations of the soil by sampler extensions range from doming of the surface without visible fracturing to doming accompanied by fracturing and the production of angular clods. Although rocks larger than 3.0 cm are abundant at VL-1 and VL-2, repeated attempts to collect rocks 0.2–1.2 cm across imbedded in soil indicate that rocks in this size range are scarce. There is no evidence that the surface sampler of VL-2, while it was pushing and nudging rocks ≈25 cm across, spalled, chipped, or fractured the rocks. Preliminary analyses of surface sampler motor currents (≈25 N force resolution) during normal sampling are consistent with cohesionless frictional soils (ϕ ≈ 36°) or weakly cohesive frictionless soils (C < 2 kN/m^2). The soil of Mars has both cohesion and friction

Jovian satellite eclipse study 2 eclipse data

The Jove satellite eclipse observations performed on April, 8 May, and 13 May, 1972 with the 200-inch Hale Telescope are reported. Spectrograms, and multichannel spectrometer data are included