X-ray fluorescence surface contaminant analyzer: A feasibility study

The bonding of liner material to the inner metal surfaces of solid rocket booster cases is adversely affected by minute amounts of impurities on the metal surface. Suitable non-destructive methods currently used for detecting these surface contaminants do not provide the means of identifying their elemental composition. The feasibility of using isotopic source excited energy dispersive X-ray fluorescence as a possible technique for elemental analysis of such contaminants is investigated. A survey is made of the elemental compositions of both D-6ac steel, a common construction material for the booster cases, and Conoco HD-2 grease, a common surface contamination. Source and detector choices that maximize signal to noise ratio in a Recessed Source Geometry are made. A Monte Carlo simulation is then made of the optimized device incorporating the latest available X-ray constants at the energy of the chosen source to determine the device's response to a D-6ac steel surface contained with Conoco HD-2 grease

Background studies in gas ionizing x ray detectors

The background response of a gas ionizing proportional x ray detector is estimated by solving the one dimensional photon transport equation for two regions using Monte Carlo techniques. The solution was effected using the SSL VAX 780 and the CRAY XMP computers at Marshall Space Flight Center. The isotropic photon energy spectrum encompassing the range from 1 to 1000 KeV incident onto the first region, the shield, is taken so as to represent the measured spectrum at an altitude of 3 mb over Palastine, Texas. The differential energy spectrum deposited in the gas region, xenon, over the range of 0 to 100 KeV is written to an output file. In addition, the photon flux emerging from the shield region, tin, over the range of 1 to 1000 KeV is also tabulated and written to a separate file. Published tabular cross sections for photoelectric, elastic and inelastic Compton scattering as well as the total absorption coefficient are used. Histories of each incident photon as well as secondary photons from Compton and photoelectric interactions are followed until the photon either is absorbed or exits from the regions under consideration. The effect of shielding thickness upon the energy spectrum deposited in the xenon region for this background spectrum incident upon the tin shield was studied

Pricing in Day-Ahead Electricity Markets with Near-Optimal Unit Commitment

This paper revisits some peculiar pricing properties of near-optimal unit commitment solutions. Previous work has found that prices can behave erratically even as unit commitment solutions approach the optimal solution, resulting in potentially large wealth transfers due to suboptimality of the solution. Our analysis considers how recently proposed pricing models affect this behavior. Results demonstrate a previously unknown property of one of these pricing models, called approximate Convex Hull Pricing (aCHP), that eliminates erratic price behavior, and therefore limits wealth transfers with respect to the optimal unit commitment solution. The absence of wealth transfers may imply fewer strategic bidding incentives, which could enhance market efficiency

Structure and dynamics of the interface between a binary hard-sphere crystal of NaCl type and its coexisting binary fluid

Molecular dynamics simulations are performed to study the [100] and [111] orientations of the crystal-melt interface between an ordered two-component hard sphere with a NaCl structure and its coexisting binary hard-sphere fluid. The diameter ratio of the two types of hard spheres making up the mixture is taken to be 0.414. This work complements our earlier interface simulations [J. Chem. Phys.116, 3410] for the same diameter ratio at lower pressures where the smaller component is immiscible in the solid and the fluid mixture coexists with a pure FCC crystal of large particles. Density profiles and diffusion coefficient profiles are presented for the AB interfacial system. We find that for this system, the transition from crystal-like to fluid-like behavior of both the density and diffusion constant profiles occurs over a narrower region than that seen in our previous studies [J. Chem. Phys. 116, 3410] of the FCC/binary fluid system. But similar to what was found in the FCC/binary fluid interface the transition region for the large particle diffusion constant is shifted about the size of the large particles toward the fluid phase relative to that for the small particles.Comment: 8 page

Process for extracting ethanol from fermentation broths for direct blending into gasoline while preserving the broth for recycling

Describes a method of producing ethanol from a fermentation source for direct blending into gasoline to form gasohol by extracting ethanol from the fermentation broth with a non-toxic solvent compatible with gasoline. The invention includes extraction outside of the fermentor and the recycling of the extracted broth back to the fermentor. An extracting column is used for the extraction and recycling and the extract can be dried before blending it with the gasoline. The preferred solvent is an alkylate