Statistical Uncertainties in Temperature Diagnostics for Hot Coronal Plasma Using the ASCA SIS

Statistical uncertainties in determining the temperatures of hot (0.5 keV to 10 keV) coronal plasmas are investigated. The statistical precision of various spectral temperature diagnostics is established by analyzing synthetic ASCA Solid-state Imaging Spectrometer (SIS) CCD spectra. The diagnostics considered are the ratio of hydrogen-like to helium-like line complexes of $Z\ge14$ elements, line-free portions of the continuum, and the entire spectrum. While fits to the entire spectrum yield the highest statistical precision, it is argued that fits to the line-free continuum are less susceptible to atomic data uncertainties but lead to a modest increase in statistical uncertainty over full spectral fits. Temperatures deduced from line ratios can have similar accuracy but only over a narrow range of temperatures. Convenient estimates of statistical accuracies for the various temperature diagnostics are provided which may be used in planning ASCA SIS observations.Comment: postscript file of 8 pages+3 figures; 4 files tarred, compressed and uuencoded. To appear in the Astrophysical Journal Letters; contents copyright 1994 American Astronomical Societ

Some Choctaw sentence structures

From the introduction: Being somewhat familiar with Longacre\u27s case grammar approach to clause analysis, (Longacre, 1974), I felt it would be helpful to apply his sentence level techniques to the study of Choctaw. Longacre presents a binary, eight-part framework within which he groups all the various types of sentence combinations. [...] I chose to concentrate on the first four deep structures which find their counterparts in formal logic. Basically, conjoining and alternation are non-sequential deep structures while temporal and implication are sequential

Nitric oxide conversion in a spark-ignited natural gas engine

A large percentage of stationary engine applications are natural gas fueled. The cleanest of these large bore engines currently produce on the order of one gram of NOx per brake-horsepower hour (g/bhp-hr) of work done. The goal of this work is to reduce these emissions to 0.1 g/bhp-hr levels. Selective NOx Recirculation (SNR) is a technology which will help achieve these 0.1 g/bhp-hr levels. SNR has been proven in gasoline and diesel engines, with up to 90% NOx conversion rates being achieved, but not much is known about its overall efficiencies when used with natural gas engines. This technique involves adsorbing NOx from an exhaust stream, then selectively desorbing the NOx into a concentrated NOx stream, which is fed back into the engine, thereby converting a percentage of the concentrated NOx into harmless gases. Understanding the NO conversion process plays a major role in optimizing the SNR technology. The NO conversion process was modeled using CHEMKIN, a chemical kinetic solver. The results showed decreasing the air-fuel ratio of the engine to slightly rich operation and adding EGR could increase the experimentally measured NO conversion of approximately 20% up to 90%