Optimum outgassing cycles for aluminum and stainless steel

Outgassing rates were measured for a modified 7075T6 aluminum and 304L stainless steel, for two degrees of finish, at temperatures of 285 deg F to 392 deg F, for times of 0.5 to 72 hours. The results were analyzed to determine optimum time and temperature cycles for outgassing. Optimum cycles were determined with and without the limitations of a graph. The graph related allowable time at temperature to a 5 percent or less reduction in room temperature properties of 7075T6 aluminum. For aluminum, within the limits set by reduction in mechanical properties, the optimum cycle tested was 40 hours at 285 deg F. Disregarding the limits, optimum outgassing was achieved at the highest temperatures and longest times tested, for both aluminum and stainless steel

Evaluation of a pulsed quasi-steady MPD thruster and associated subsystems

The performance of quasi-steady magnetoplasmadynamic (MPD) thrusters at high power levels is discussed. An axisymmetric configuration is used for the MPD thruster, with various cathode and anode sizes, over a wide range of experimental conditions. Thrust is determined from impulse measurements with current waveforms, while instantaneous measurements are made for all other variables. It is demonstrated that the thrust produced has a predominately self-magnetic origin and is directly proportional to the square of the current. The complete set of impulse measurement data is presented

Quasi-steady MPD propulsion at high power Final technical report

Quasi-steady MPD propulsion at power levels in range 1 to 10 megawatt

Refinement and Validation of a Real-time Airborne System for Remotely Sensing Ocean Surface using Communication Satellite Signals

The ability to remotely sense ocean wave heights and wind speed by measuring the reflected Radio Frequency (RF) signals from the ocean’s surface has been demonstrated in previous research projects. The recording systems for these research projects collected and stored unmodified RF signals and then analyzed the data through post-processing. Several disadvantages to this approach include large requirements for data storage and lengthy post-processing time. To assist in the creation of a suitable platform for an airplane-based application, a new system was designed which features real-time processing of the RF signals. This system captures two RF signals in the 2.4 GHz regions (direct and reflected), calculates the cross-correlation between the two signals and then outputs the result to a PC. Due to the time-consuming nature of the cross-correlation algorithm, a FPGA based implementation of the system was chosen to conform to the real-time constraints of the system. In this project, previously created Verilog source code for the system was debugged, improved and verified. This project also developed a method to test the system by using several 110-foot sections of RG6 Coaxial Cables. These cables induced a physical delay in the reflected channel, simulating the application’s conditions, in order to cause a shift in the correlation peak. The results are discussed as well as suggestions for future improvements

Remote sensing using I-Band and S-Band signals of opportunity

Measurement of soil moisture, especially the root zone soil moisture, is important in agriculture, meteorology, and hydrology. Root zone soil moisture is concerned with the first meter down the soil. Active and passive remote sensing methods used today utilizing L-band(1-2GHz) are physically limited to a sensing depth of about 5 cm or less. To remotely sense the soil moisture in the deeper parts of the soil, the frequency should be lowered. Lower frequencies cannot be used in active spaceborne instruments because of their need for larger antennas, radio frequency interference (RFI), and frequency spectrum allocations. Ground-based passive remote sensing using I-band(0.1-1GHz) signals of opportunity provides the required sensing depth and solves the problems that come with the spaceborne remote sensing instruments using I-band reflectometry. A dual monopole antenna setup was used with one on the ground for direct signal and one 30m above ground for the reflected signal. The reflectivity and therefore the soil moisture was obtained from the differences between direct and reflected signals. Initially, an S-band (2-3GHz) signal was used as a proof of concept and its ease of implementation because of its higher transmitted power and stationary satellite. This experiment provides conclusions about the root zone soil moisture based on our observation and comparison of direct and reflected satellite signals of two different frequency bands and determination of reflectivity

Using P-band Signals of Opportunity Radio Waves for Root Zone Soil Moisture Remote Sensing

Retrieval of Root Zone Soil Moisture (RZSM) is important for understanding the carbon cycle for use in climate change research as well as meteorology, hydrology, and precision agriculture studies. A current method of remote sensing, GNSS-R uses GPS signals to measure soil moisture content and vegetation biomass, but it is limited to 3-5 cm of soil penetration depth. Signals of Opportunity (SoOp) has emerged as an extension of GNSS-R remote sensing using communication signals. P-band communication signals (370 MHz) will be studied as an improved method of remote sensing of RZSM. P-band offers numerous advantages over GNSS-R, including stronger signal strength and deeper soil penetration. A SoOp instrument was installed on a mobile antenna tower in a farm field at Purdue University in West Lafayette, IN. An additional half-wave dipole antenna, as well as corresponding modifications to the experiment’s front-end box, was included to capture horizontally-polarized reflected P-band signals throughout a corn growth season. By measuring the reflected signal power off the soil over time, soil moisture and above-ground biomass can be measured. Soil moisture and vegetation biomass change the soil’s dielectric reflection coefficient and thus affect its reflectivity properties. It is expected that there will be strong correlation between reflected signal strength and soil moisture. Data will be compared against soil moisture measurements from in-situ soil sensors. The data obtained will be used to verify existing analytical soil moisture and above-ground biomass models. In addition, these results will be used to build an airborne and/or space-based remote sensing instrument

Canonical and kinetic forms of the electromagnetic momentum in an ad hoc quantization scheme for a dispersive dielectric

An ad hoc quantization scheme for the electromagnetic field in a weakly dispersive, transparent dielectric leads to the definition of canonical and kinetic forms for the momentum of the electromagnetic field in a dispersive medium. The canonical momentum is uniquely defined as the operator that generates spatial translations in a uniform medium, but the quantization scheme suggests two possible choices for the kinetic momentum operator, corresponding to the Abraham or the Minkowski momentum in classical electrodynamics. Another implication of this procedure is that a wave packet containing a single dressed photon travels at the group velocity through the medium. The physical significance of the canonical momentum has already been established by considerations of energy and momentum conservation in the atomic recoil due to spontaneous emission, the Cerenkov effect, the Doppler effect, and phase matching in nonlinear optical processes. In addition, the data of the Jones and Leslie radiation pressure experiment is consistent with the assignment of one ?k unit of canonical momentum to each dressed photon. By contrast, experiments in which the dielectric is rigidly accelerated by unbalanced electromagnetic forces require the use of the Abraham momentum.Comment: 21 pages, 1 figure, aip style, submitted to PR