Ichthyofaunal Diversification and Distribution in the Big Creek Watershed, Craighead and Greene Counties, Arkansas

Big Creek is a relatively small deltaic stream, in northeastern Arkansas, in an area of intense cultivation. Recently it has been dredged in the interest of flood control. Lost Creek and Mud Creek are the major tributaries of Big Creek and collectively drain the Big Creek watershed. The streams were found to have relatively low alkalinity, moderate carbon dioxide, adequate oxygen values, and relatively high turbidity. Channeling of Big Creek and Lost Creek has effectively destroyed distinct pool-riffle biocies and reduced the number of acceptable spawning areas. Lost Creek, also, receives effluent from residential dwellings, a secondary treatment sewage plant, and a meat rendering plant. Mud Creek, in the absence of channeling and deleterious effects of effluents, provided a relatively greater diversity of habitat than did Big Creek or Lost Creek

Quantitative gated blood pool tomographic assessment of regional ejection fraction: Definition of normal limits

AbstractObjective. Our aim was to select a method of analysis for gated blood pool tomography that reduced variability in a group of normal subjects, allowed comparison with normal limit files and displayed results in the bull's-eye format.Background. Abnormalities in left ventricular function may not be accurately detected by measures of global function because hyperkuiesia in normal regions may compensate for abnormal regional function. Gated blood pool tomography acquires threedimensional data and offers advantages over other noninvasive modalities Tor quantitative assessment of global and regional function.Methods. Alternative methods for selecting the ventricular axis, calculating regional ejection fraction and choosing the number of ventricular divisions were studied In 15 normal volunteers to select the combination of parameter that produced the lowest variability in quantitative regional ejection fraction. Methods for quantitative comparison, of regional ejection fraction with normal limit files and for display in the bull's-eye format were also examined.Results. A fixed axis (the geometric center of the ventricle defined for end-diastole and used for end-systole) gave ejection fractions that were significantly higher in the lateral wall versus in the septum, 82 ± 8 (mean ± 1 SD) versus 39 ± 17 (p < 0.001) at the midcavity and 66 ± 11 versus 21 ± 20 (p < 0.001) at the base. A floating axis system (axis defined individually for end-diastole and end-systole and realigned at the center) gave more uniform regional ejection fraction: 63 ±6 versus 64 ± 8 (p = NS) at the midcavity and 44 ± 16 versus 45 ± 15 (p = NS) at the base. The coefficient of variability for regional ejection fraction was consistently lower using a floating axis. Calculating regional ejection fraction by dividing the regional stroke volume by the enddiastollc volume of the region gave a lower coefficient of variability and a more easily understood value than dividing the regional stroke volume by the total end-diastolic volume of the ventricle. Although the variability was lower using five versus nine ventricular divisions, nine regions offer greater spatial resolution. Comparison of regional ejection fraction with normal data identified regions > 2.5 SD below the mean as abnormal. We described the two-dimensional bull's-eye format as a method for displaying the regional three-dimensional data and illustrated abnormalities in patients with prior myocardial infarction.Conclusions. Gated blood pool tomography performed using a floating axis system, regional stroke volume calculation of ejection fraction and nine regions uses all the three-dimensional blood pool data to calculate regional ejection fraction, allow quantitative comparison with normal limit tiles, display the functional data in the two-dimensional bull's-eye format and demonstrate abnormalities in patients with myocardial infarction

Propulsion System for Very High Altitude Subsonic Unmanned Aircraft

This paper explains why a spark ignited gasoline engine, intake pressurized with three cascaded stages of turbocharging, was selected to power NASA's contemplated next generation of high altitude atmospheric science aircraft. Beginning with the most urgent science needs (the atmospheric sampling mission) and tracing through the mission requirements which dictate the unique flight regime in which this aircraft has to operate (subsonic flight at greater then 80 kft) we briefly explore the physical problems and constraints, the available technology options and the cost drivers associated with developing a viable propulsion system for this highly specialized aircraft. The paper presents the two available options (the turbojet and the turbocharged spark ignited engine) which are discussed and compared in the context of the flight regime. We then show how the unique nature of the sampling mission, coupled with the economic considerations pursuant to aero engine development, point to the spark ignited engine as the only cost effective solution available. Surprisingly, this solution compares favorably with the turbojet in the flight regime of interest. Finally, some remarks are made about NASA's present state of development, and future plans to flight demonstrate the three stage turbocharged powerplant