• Economic Analysis Of Alternatives For Railroad Vegetation Control

      Chouinard, Jill Suzanne (1990)
      A survey was distributed to 174 railroads throughout the United States and selected foreign countries. The purpose of the survey was to determine which methods of vegetation control were used along railroad rights-of-way. Cost data were gathered from the railroads responding to the survey and the data were analyzed and compared to an independent cost analysis. Vegetation control by herbicide application, brush cutting, ballast regulating, reballasting, undercutting, and hand clearing were examined. The least expensive alternatives (in average U.S. data base, 1991 dollar base) were vegetation control with a ballast regulator at a cost of $330 per mile, herbicide application at \$485 per mile, and brush cutting with a cost of $554 per mile. An integrated vegetation management program should be developed using a combination of these methods to get the most effective and economic vegetation control. <p>
    • The Nutrient Flow System: Control Of Nutrient Availability And Measurement Of Ion Uptake

      Bishop, Daniel R.; Kokjer, Ken (1990)
      An instrumentation and control system was built to maintain a constant nutrient supply to plants in flowing solution culture. The microcomputer based system controls the concentration of mineral nutrients, pH, root temperature, and water level. The nutrient ion concentrations controlled by the computer are nitrate, potassiuum, and ammonium. Ion-specific electrodes used as sensors are automatically calibrated before each measurement. Computer controlled valve manifolds and a 16-channel peristaltic pump mix aliquots of nutrient solution with ionic strength adjuster for improved electrode operation. A mathematical analysis of the performance of the Nutrient Flow System shows how the error introduced in system components contributes to error in measurements, and how experimental parameters affect accuracy. Results of plant growth trials are given, and statistical techniques for evaluating growth trial results are discussed. Over a sixteen day experiment with a target concentration of 1.0 $\times$ 10$\sp{-4}$-M NO$\sbsp{3}{-}$, the variance of the concentration was 2.4 $\times$ 10$\sp{-6}$. The uptake over the experiment was 91.6 grams of nitrate. There was a 1.5% discrepancy between actual uptake and the uptake calculated by the system. <p>