The spatial and temporal subsidence variability of the East Mesa Geothermal Field,California, USA,and its potential impact on the All American Canal System

The spatiotemporal variability of subsidence around the East Mesa Geothermal Field (EMGF) near the All American Canal (AAC) has been measured using 30 temporally averaged interferograms from 1992 to 2000. Deformation rate maps from two shorter time periods indicated the maximum subsidence rate of the EMGF was reduced from??43 mm year^?1 (1992–1997) to??34 mm year^?1 (1996–2000) corresponding to decreasing net geothermal water production. The maximum subsidence on the East Highline Canal was??9.5 ± 0.5 and??2.4 ± 0.8 cm for each shorter time period. Interferometric synthetic aperture radar (InSAR) stacking demonstrated its utility in monitoring subsidence of the canal caused by the nearby geothermal plant at regional coverage superior to ground levelling networks. Such data on the subsidence of surface and subsurface hydrodynamics along the US–Mexico border are scarce, and are particularly significant in a zone of present and likely future acute water resource management sensitivity.     

Calorimeters with proximity-effect thermometers and lead and tin absorbers

Taking advantage of the low critical temperatures of proximity-effect phase transition thermometers, superconductors with low Debye temperatures can be used as absorber materials for calorimetric detectors. We performed experiments with lead and tin absorbers of a mass of about 1 g. The energy resolutions for 6 keV X-rays are 1000 eV and 230 eV FWHM, respectively. A model which includes the effect of both thermal and non-thermal phonons explains the measured pulse shapes. The observed heat capacity of the absorbers agrees with that given by the Debye law. A comparison of heat pulses and of radiation induced pulses shows a thermalization efficiency close to 100%. No evidence for trapping of energy as quasiparticles is observed.     

A chopped Hall sensor with small jitter and programmable "True Power-on" function

A chopped Hall sensor for camshaft applications is presented which provides a programmable "True Power-on" switching level effective after the power-up phase. The proposed chopping technique and self-compensation methods for temperature drift and technology spread provide a correct output state immediately after power-on even at zero speed of the target wheel. The circuits improve the magnetic offsets from 5 to 10 mT to below 200 /spl mu/T in a bandwidth of 30 kHz and stabilize the spread of the magnetic switching points from 20% to <2% in a temperature range from -40/spl deg/C to 175/spl deg/C. The novel combination of chopping and enhanced digital self-calibration algorithm adjusts the magnetic switching point and improves phase accuracy to <0.5/spl deg/, independent of air gap variations between sensor and wheel. An end-of-line calibration for the customer is implemented using surface micromachined cavity fuses which offer a reliable function higher than 195/spl deg/C.     

Electrochemiluminescent metallopolymer coatings: combined light and current detection in flow injection analysis

The application of thin films of the metallopolymer [Ru(bpy)2PVP10]2+ for the electrochemiluminescent (ECL) detection of oxalate in a flow injection analysis system is reported, where bpy is 2,2'-bipyridyl and PVP is poly(4-vinylpyridine). Immobilization of the ECL reagent means that it can be regenerated in situ, eliminating the need to constantly deliver it to the reaction zone. Electrochemically generated Ru3+ reacts with the analyte to form the excited-state [Ru2+]*, which luminesces at 610 nm. The reaction is optimal at low pH, where the layer is swollen and homogeneous charge transport through the layer is more facile. Unlike traditional approaches, we simultaneously monitor both the amperometric and luminescent response of the modified electrode. The precision of both signals is similar at approximately 2% (n = 10). However, the ECL response has a larger dynamic range extending from the low-micromolar to high-millimolar range and a lower limit of detection, approximately 0.2 microM or 4 pmol of oxalate injected. The ECL approach displays excellent selectivity for oxalate over a wide range of potential interferences including oxygen, amines, iron sulfate, ammonium nitrate, urea, and glucose. Ascorbic acid represents the most significant ECL interference. However, the signal observed for a 1 mM solution of ascorbic acid is still only 2.6% of the response observed for the injection of a similar concentration of oxalate.     

Limitations of the Luneburg lens as a calibration target for adual-antenna radar system

The Luneburg lens, which is commonly used to calibrate radar scatterometers, may not be appropriate for calibration of dual-antenna systems. Theory and results from measurements of the Luneburg lens reradiation pattern indicate that gross errors may be incurred when using the lens to calibrate a dual-antenna system. Measurements of the reradiation pattern indicate that special attention must be paid to the angular separation of the antennas when using the lens to calibrate a dual-antenna radar system. The angular separation of the antennas must be less than the half-power beamwidth of the lens to ensure accurate repeatable measurements. A formula for estimating the half-power beamwidth is given