Nonparametric measures of the impact of public research expenditures on Australian broadacre agriculture

Nonparametric methods are used to measure the impact of public research expenditures on Australian broadacre agriculture over the 1953–94 period. Results using both unrestricted and 30‐year lagged specifications of the research impacts on productivity suggest that while certain aspects of the nonparametric multi‐input/output technologies are quite robust to alternative specifications (in particular, the associated Malmquist total factor productivity indexes), other aspects are less stable (in particular, the indexes on input and, to a lesser extent, output biased technical change). Internal rates of return to research expenditures on Australian broadacre agriculture are estimated to be in the 12 per cent to 20 per cent range.Crop Production/Industries, Research and Development/Tech Change/Emerging Technologies,

Laser-Induced Fluorescence of Singly-Charged Xenon Inside a 6-kW Hall Thruster

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77282/1/AIAA-2009-5355-837.pd

Two-Axis Laser-Induced Fluorescence of Singly-Charged Xenon inside a 6-kW Hall Thruster

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90653/1/AIAA-2011-1015-640.pd

Neutral Flow Evolution in a Six-Kilowatt Hall Thruster

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90645/1/AIAA-54141-803.pd

Hybrid-PIC Modeling of a High-Voltage, High-Specific-Impulse Hall Thruster

The primary life-limiting mechanism of Hall thrusters is the sputter erosion of the discharge channel walls by high-energy propellant ions. Because of the difficulty involved in characterizing this erosion experimentally, many past efforts have focused on numerical modeling to predict erosion rates and thruster lifespan, but those analyses were limited to Hall thrusters operating in the 200-400V discharge voltage range. Thrusters operating at higher discharge voltages (V(sub d) >= 500 V) present an erosion environment that may differ greatly from that of the lower-voltage thrusters modeled in the past. In this work, HPHall, a well-established hybrid-PIC code, is used to simulate NASA's High-Voltage Hall Accelerator (HiVHAc) at discharge voltages of 300, 400, and 500V as a first step towards modeling the discharge channel erosion. It is found that the model accurately predicts the thruster performance at all operating conditions to within 6%. The model predicts a normalized plasma potential profile that is consistent between all three operating points, with the acceleration zone appearing in the same approximate location. The expected trend of increasing electron temperature with increasing discharge voltage is observed. An analysis of the discharge current oscillations shows that the model predicts oscillations that are much greater in amplitude than those measured experimentally at all operating points, suggesting that the differences in oscillation amplitude are not strongly associated with discharge voltage

Hybrid-PIC modeling of a high-voltage, high-specific-impulse Hall thruster

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106478/1/AIAA2013-3887.pd

Frequency Following Imaging of Electric Fields from Resonant Superconducting Devices using a Scanning Near-Field Microwave Microscope

We have developed a scanning near-field microwave microscope that operates at cryogenic temperatures. Our system uses an open-ended coaxial probe with a 200 mm inner conductor diameter and operates from 77 to 300 K in the 0.01-20 GHz frequency range. In this paper, we present microwave images of the electric field distribution above a Tl2Ba2CaCu2O8 microstrip resonator at 77 K, measured at several heights. In addition, we describe the use of a frequency-following circuit to study the influence of the probe on the resonant frequency of the device.Comment: 4 pages, postscript file with 6 figures conference proceeding for the Applied Superconductivity Conference 199

Superconducting Material Diagnostics using a Scanning Near-Field Microwave Microscope

We have developed scanning near-field microwave microscopes which can image electrodynamic properties of superconducting materials on length scales down to about 2 $\mu$m. The microscopes are capable of quantitative imaging of sheet resistance of thin films, and surface topography. We demonstrate the utility of the microscopes through images of the sheet resistance of a YBa2Cu3O7-d thin film wafer, images of bulk Nb surfaces, and spatially resolved measurements of Tc of a YBa2Cu3O7-d thin film. We also discuss some of the limitations of the microscope and conclude with a summary of its present capabilities.Comment: 6 pages with 9 figures, Proceedings of the Applied Superconductivity Conference 199

Laser-Induced Fluorescence of Singly-Charged Xenon in a 6-kW Hall Thruster Plume

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76708/1/AIAA-2008-5102-585.pd

The Stability of LSF-YSZ Electrodes Prepared by Infiltration

Composite electrodes were prepared by adding 40 wt % La0.8Sr0.2FeO3 (LSF) into porous yttria-stabilized zirconia (YSZ) and their performance was studied as a function of time and calcination temperature. X-ray diffraction (XRD) patterns of the LSF-YSZ composites indicated an expanded lattice parameter after calcination above 1523 K, suggesting that Zr reacted with the LSF to form a Zr-doped perovskite; but XRD provided no evidence for reaction between LSF and YSZ after calcination at 1373 K or after operation for 1000 h at 973 K and 700 h at 1073 K. A composite of 40 wt % La0.8Sr0.2Fe0.9Zr0.1O3 in YSZ showed reasonable performance at 973 K, with an area-specific resistance (ASR) of 0.22 Ω cm2. Based on symmetric-cell measurements, electrodes calcined at 1123 K showed an initial ASR of 0.13 Ω cm2 at 973 K but this increased linearly with time to 0.55 Ω cm2 after 2500 h at 973 K. However, the ASR depended strongly on current density, decreasing dramatically under both anodic and cathodic polarization. Electrodes calcined at 1373 K showed an ASR of 2.5 Ω cm2 at 973 K but this value also decreased dramatically under polarization. Scanning electron microcopy images demonstrate that aging at 973 K and calcination at 1373 K cause significant sintering of the LSF. It is therefore suggested that deactivation is caused by morphological changes, rather than solid-state reactions, with a dense layer of LSF forming over the YSZ substrate