Baffle aperture design study of hollow cathode equipped ion thrusters

A simple theoretical model which can be used as an aid in the design of the baffle aperture region of a hollow cathode equipped ion thruster was developed. An analysis of the ion and electron currents in both the main and cathode discharge chambers is presented. From this analysis a model of current flow through the aperture, which is required as an input to the design model, was developed. This model was verified experimentally. The dominant force driving electrons through the aperture was the force due to the electrical potential gradient. The diffusion process was modeled according to the Bolm diffusion theory. A number of simplifications were made to limit the amount of detailed plasma information required as input to the model to facilitate the use of the model in thruster design. This simplified model gave remarkably consistant results with experimental results obtained with a given thruster geometry over substantial changes in operating conditions. The model was uncertain to about a factor of two for different thruster cathode region geometries. The design usefulness was limited by this factor of two uncertainty and by the accuracy to which the plasma parameters required as inputs to the model were specified

Effectiveness of an instructional packet on supervised occupational experience programs as evaluated by agricultural knowledge achievement of Iowa vocational agriculture students

The purpose of this study was to evaluate the impact of an instructional packet on supervised occupational experience programs in terms of student agricultural knowledge achievement after two and one-half years. The study was a posttest only control group (true experimental) design. Students (in 16 schools that had been randomly assigned to the experimental treatment group) provided data for comparison with data from students in the 16 schools that were similarly assigned to the control treatment group. The experimental treatment consisted of access to (and inservice instruction for teachers in the use of) an instructional packet developed to help beginning students select and plan individual SOE programs. The control group teachers taught their normal instructional units on SOE to their beginning classes;Four instruments were used to evaluate the effectiveness of the instructional packet: an Involvement in Agriculture Inventory and the Animal Science, Plant and Soil Science, and Mechanics subtests of the Agribusiness Achievement Test. Previously acquired data concerning student SOE knowledge, attitude, and planning were used in the analysis of data. Data analysis procedures employed included: frequencies and counts, student\u27s t-test of mean differences, analysis of variance, and Duncan\u27s Multiple Range Test for Mean Differences;Major findings of the study were: (1) The SOE packet was effective in helping students achieve, (2) SOE is an effective teaching method, (3) The primary types of SOE possessed by juniors observed in Iowa (ownership of animals/crops, work on farms other than home, work in off-farm agribusiness, and school projects other than normal classroom and shop activities) comprised 95% of reported SOE participation, (4) these Iowa juniors have achieved significantly more agricultural knowledge than their 1972 national counterparts, (5) Students achieved more knowledge in mechanics and animal science than in plant and soil science, (6) Teacher stability (whether in 1978 teacher continued to teach at that school) had no significant impact on the knowledge achievement of students, and (7) Beginning student knowledge of SOE (after instruction in the freshman year of vocational agriculture) was determined to be a reliable predictor of student knowledge achievement for those students as juniors two and one-half years later

An approach to the parametric design of ion thrusters

A methodology that can be used to determine which of several physical constraints can limit ion thruster power and thrust, under various design and operating conditions, is presented. The methodology is exercised to demonstrate typical limitations imposed by grid system span-to-gap ratio, intragrid electric field, discharge chamber power per unit beam area, screen grid lifetime, and accelerator grid lifetime constraints. Limitations on power and thrust for a thruster defined by typical discharge chamber and grid system parameters when it is operated at maximum thrust-to-power are discussed. It is pointed out that other operational objectives such as optimization of payload fraction or mission duration can be substituted for the thrust-to-power objective and that the methodology can be used as a tool for mission analysis

Performance Data from a Wind-Tunnel Test of Two Main-rotor Blade Designs for a Utility-Class Helicopter

An investigation was conducted in the NASA Langley Transonic Dynamics Tunnel to evaluate an advanced main rotor designed for use on a utility class helicopter, specifically the U.S. Army UH-60A Blackhawk. This rotor design incorporated advanced twist, airfoil cross sections, and geometric planform. For evaluation purposes, the current UH-60A main rotor was also tested and is referred to as the baseline blade set. A total of four blade sets were tested. One set of both the baseline and the advanced rotors were dynamically scaled to represent a full scale helicopter rotor blade design. The remaining advanced and baseline blade sets were not dynamically scaled so as to isolate the effects of structural elasticity. The investigation was conducted in hover and at rotor advance ratios ranging from 0.15 to 0.4 at a range of nominal test medium densities from 0.00238 to 0.009 slugs/cu ft. This range of densities, coupled with varying rotor lift and propulsive force, allowed for the simulation of several vehicle gross weight and density altitude combinations. Performance data are presented for all blade sets without analysis; however, cross referencing of data with flight condition may be useful to the analyst for validating aeroelastic theories and design methodologies as well as for evaluating advanced design parameters

ECONOMIC EFFECTS OF MINNESOTA PEATLAND DEVELOPMENT

Existing peatland development and future uses for peat are described and evaluated in this report. Scenarios for future development of the study area peat industry are described in terms of employment, earnings, capital investment, and value of production. Forecasts of the potential impacts of peatland development on regional industry production, employment, earnings, and population are presented. These impacts are determined by using SIMLAB, an acronym for a regional socio-economic computer model developed at the University of Minnesota for quantitative analysis of the direct, indirect and induced socio-economic effects of events like peatland development.Land Economics/Use,

ECONOMIC EFFECTS OF COPPER-NICKEL DEVELOPMENT IN NORTHEAST MINNESOTA

Computer simulations of industry gross output, employment and earnings changes associated with alternative copper-nickel development scenarios are presented in this report. The direct and indirect economic effects of seven development scenarios are projected for a mining impact Study Area in St. Louis County, Minnesota.Community/Rural/Urban Development, Resource /Energy Economics and Policy,

Reduction of blade-vortex interaction noise using higher harmonic pitch control

An acoustics test using an aeroelastically scaled rotor was conducted to examine the effectiveness of higher harmonic blade pitch control for the reduction of impulsive blade-vortex interaction (BVI) noise. A four-bladed, 110 in. diameter, articulated rotor model was tested in a heavy gas (Freon-12) medium in Langley's Transonic Dynamics Tunnel. Noise and vibration measurements were made for a range of matched flight conditions, where prescribed (open-loop) higher harmonic pitch was superimposed on the normal (baseline) collective and cyclic trim pitch. For the inflow-microphone noise measurements, advantage was taken of the reverberance in the hard walled tunnel by using a sound power determination approach. Initial findings from on-line data processing for three of the test microphones are reported for a 4/rev (4P) collective pitch control for a range of input amplitudes and phases. By comparing these results to corresponding baseline (no control) conditions, significant noise reductions (4 to 5 dB) were found for low-speed descent conditions, where helicopter BVI noise is most intense. For other rotor flight conditions, the overall noise was found to increase. All cases show increased vibration levels

Bunch Of Heather : March and Two Step

https://digitalcommons.library.umaine.edu/mmb-ps/1283/thumbnail.jp