A shape memory alloy adaptive tuned vibration absorber: design and implementation

In this paper a tuned vibration absorber (TVA) is realized using shape memory alloy (SMA) elements. The elastic modulus of SMA changes with temperature and this effect is exploited to develop a continuously tunable device.A TVA with beam elements is described, a simple two-degree-of-freedom model developed and the TVA characterized experimentally. The behaviour during continuous heating and cooling is examined and the TVA is seen to be continuously tunable. A change in the tuned frequency of 21.4% is observed between the cold, martensite, and hot, austenite, states. This corresponds to a change in the elastic modulus of about 47.5%, somewhat less than expected.The response time of the SMA TVA is long because of its thermal inertia. However, it is mechanically simple and has a reasonably good performance, despite the tuning parameters depending on the current in a strongly nonlinear way

Five Gallons in a Ten Gallon Hat: Groundwater Sustainability in Texas

Despite the hopes and desires of scientists, engineers, and planners, the projected future of groundwater production in Texas is unsustainable. About 95 percent of locally-expressed desired future conditions are based on water-level declines, groundwater is currently being produced at 1.8 times the maximum sustainable amount, and groundwater is expected to be produced 2.4 times the maximum sustainable amount. However, Texas has an opportunity to consider groundwater sustainability since current production for all aquifers excluding the Ogallala Aquifer is only 80 percent of the maximum sustainable amount of production.To better understand how groundwater is produced sustainably, I identified five types of sustainable groundwater management in Texas: (1) hydrologically-forced, (2) court-forced, (3) legislatively-forced, (4) desire-driven, and (5) de facto. There is also the situation where it is politically difficult to achieve sustainability, generally when production far exceeds sustainable production, thus requiring controversial production reductions. Hydrologically-forced sustainable production seems to only occur when aquifers are small and highly productive. In Texas, part of the Edwards and Gulf Coast aquifers are sustainably managed due to court and legislative forcing, the latter in response to the former. Through the establishment of desired future conditions, a dozen or so groundwater conservation districts have explicitly expressed a desire to manage groundwater resources sustainably. And there are cases of aquifers being produced sustainably without any management action--at least for now. But there are also many aquifers not produced sustainably because production or permits have exceeded maximum sustainable production.Based on the results of this study, I recommend that (1) groundwater conservation districts include decadal water budgets in explanatory reports for desired future conditions or the Texas Water Development Board include these budgets as part of the delivery of modeled available groundwater numbers, (2) the Texas Water Development Board carefully consider the process of estimating maximum sustainable production if and when they are required to provide those estimates, and (3) the Legislature consider requiring maximum sustainable production as another factor for groundwater conservation districts to consider when establishing desired future conditions

Calibration of a Silver Detector using a PuBe Source

During the initial design of the Field Reversed Compression and Heating Experiment (FRCHX), magnetohydrodynamic simulations performed by Los Alamos National Laboratory using MACH2 predicted a neutron yield on the order of 1012 neutrons. However, Air Force Research Laboratory (AFRL) measurements indicate a total of 107-108 neutrons are generated from the FRCHX. A PuBe source was used to create a burst of neutrons to calibrate an AFRL silver detector based on distance to determine if the four order of magnitude discrepancy was cause by an improperly calibrated detector. It was determined that the calibration equation in use by AFRL for the silver detectors was correct within error at most points compared to this work. An alternate calibration equation FPuBe = 12.2D2 + 3020D where D is the distance in inches from the source to the front face of the silver detector, was found using least squares techniques to reduce the residuals of the data collected using the PuBe source. The silver detectors were properly calibrated which does not account for the large order of magnitude difference observed between experiment and simulation of the FRCHX

Emissions testing of two recreational marine engines with water contact in the exhaust stream

Recreational marine engine operation effects water quality as well as air quality. Significant quantities of hydrocarbons are discharged into the rivers, lakes, and estuaries used as recreational boating waters. In order to investigate the impact of recreational marine engine operation on water quality, a MerCruiser 3.0LX four-cylinder four-stroke inboard engine and a Mercury 650 two-cylinder two-stroke outboard engine were tested using EPA required certification procedures. Both engines were tested with exhaust gas/cooling water mixing (scrubbing) in the exhaust stream using both freshwater and saltwater. Additionally, the inboard engine was tested without exhaust scrubbing. Gaseous emissions (HC, NOx, CO, and CO2) from the engines were continuously measured using a constant volume sampling system. Both exhaust gas and cooling water samples were collected and speciated for hydrocarbon species present. In addition, carbonyl compounds were collected by diverting a portion of the exhaust stream through 2,4-dinitrophenylhydrazine (DNPH) charged cartridges. Chromatography methods were used for species identification. Detailed descriptions of the testing apparatus, equipment, and analysis procedures used are included. Results for gaseous emissions, carbonyl compounds, and aqueous samples are reported. The mass ratios of hydrocarbons to carbon dioxide gaseous emission for the MerCruiser and Mercury engines were approximately 0.0046 and 0.55 respectively. These results show that concerns over gaseous hydrocarbon emissions from these sources are warranted. Additionally, high levels of acetone were detected in gaseous emissions from the MerCruiser engine while operated with exhaust scrubbing

Targeted Germanium Ion Irradiation of Aluminum Gallium Nitride/Gallium Nitride High Electron Mobility Transistors

Microscale beams of germanium ions were used to target different locations of aluminum galliumnitride/gallium nitride (AlGaN/GaN) high electron mobility transistors (HEMTs) to determine location dependent radiation effects. 1.7 MeV Ge ions were targeted at the gap between the gate and the drain to observe displacement damage effects while 47 MeV Ge ions were targeted at the gate to observe ionization damage effects. Electrical data was taken pre, during, and post irradiation. To separate transient from permanent degradation, the devices were characterized after a room temperature anneal for at least 30 days. Optical images were also analyzed pre and post irradiation. This is the first use of localized dynamic irradiation testing has been used to compare AlGaN/GaN HEMT performance to the results of stress testing via in situ measurements of the gate and drain currents. The 6 MV Tandem Accelerator at Sandia National Laboratories using the Micro-ONE system was used to induce displacement and ionization damage. Displacement damage was caused by 1.7 MeV Ge ions targeting the gate-drain gap of ten HEMTs in the off, on, and semi-on bias states where a fluence dependent delayed response between ion deposition and gate current degradation in the semi-on and on bias state was observed. The delayed response was also observed in the drain current degradation when biased in the semi-on state, while occurring immediately in the on state. Ionization damage was induced by 47 MeV Ge ions targeting the gate region in the semi-on bias state where gate current degradation occurred during the initial irradiation of the gate active region. Drain current degradation occurred in both the initial and subsequent irradiations. Pre and post irradiation output and transfer performance characteristics indicate drain current and transconductance degradation for both experiments in all bias states. No threshold voltage shift was observed during the displacement damage experiment with 1.7 MeV Ge ions. During the ionization experiment, the threshold voltage increased after the initial irradiation with 2 x 1010 cm-2 47 MeV Ge ions across the length of the gate. Subsequent irradiation over the same location and after a 60 day room temperature anneal did not change this threshold voltage shift and the decrease in the drain current and transconductance persisted, indicating permanent damage. The same performance characteristics changes have been associated with reliability stress testing causing similar effective damage in both the gate-drain gap and the gate regions. The observed degradation in device characteristics are consistent with the inverse piezoelectric effect in the displacement damage experiment and charge trapping in the gate region in the ionization experiment. These results show that radiation induced degradation can be captured by using a targeted ion beam in order to determine location dependent fluence limits, thereby informing both reliability and radiation hardness models

A high level noise blanker RF amplifier system for the UHF band

The design and construction of a high level noise blanker and RF amplifier system as used in RFI measurement work is presented. This RFI work is part of the Shipboard RFI in UHF SATCOM project sponsored by Naval Electronic Systems Command. The system requirements are discussed providing a basis for deriving the system specifications. The design of the solid state blanker is presented in detail, along with tests performed on the completed system. Electromagnetic compatibility of the unit with the working environment is considered in the design and in the special construction techniques employedPrepared for: Naval Electronic Systems Command, PME 106, Washington, D.C. 20302.http://archive.org/details/highlevelnoisebl76106maceA task under the Shipboard RFI in UHF SATCOM Project.N