Feedback Control of Particle Positions using Electric Fields and Chemical Gradients

Programmable self-assembly is a promising route to new biomaterial and metamaterial synthesis methods. An important step towards programmable self-assembly is moving component parts to desired locations. We do this by designing and simulating a controller that modifies an external field to move particles on desired paths. We first design a controller using electric fields by modifying established methods, then we apply the insights gained from the electric field controller to a chemical controller that uses model predictive control

Interannual variability in North American grassland biomass/productivity detected by SeaWinds scatterometer backscatter

We analyzed 2000–2004 growing-season SeaWinds Ku-band microwave backscatter and MODIS leaf area index (LAI) data over North America. Large anomalies in mid-growing-season mean backscatter and LAI, relative to 5-year mean values, occurred primarily in the western Great Plains; backscatter and LAI anomalies had similar spatial patterns across this region. Backscatter and LAI time series data for three ∼103 km2 regions in the western Great Plains were strongly correlated (r2 ∼ 0.6–0.8), and variability in mid-growing season values was well-correlated with annual precipitation (October through September). The results indicate that SeaWinds backscatter is sensitive to interannual variability in grassland biomass/productivity, and can provide an assessment that is completely independent of optical/near-infrared remote sensing instruments

A high resolution gravity survey for the detection of Pleistocene aquifers underlying the Fort Berthold Indian Reservation, North Dakota

A high resolution gravity survey was performed over portions of McLean, Mountrail, and Ward Counties in central North Dakota during the fall and winter of 1990-1991. The study was performed to locate and map Pleistocene sand and gravel aquifers. Well data indicate that aquifers beneath the study area range in thickness from 1 to 60 meters. The Bouguer gravity anomalies resulting from these shallow aquifers was estimated to be on the order of 1 to 2 mgals. Previous studies have focused on available well data and by mapping topographic lows. Due to the inferential nature of these studies, the detailed gravity method was chosen as an attractive and cost-effective method of further defining these aquifers. Station locations were established at 0.4 km spacings along accessible roads using the Global Positioning Satellite system. Of the 4000 stations that were occupied, approximately 2700 station locations were satisfactorily produced. The gravity readings were obtained by using three La Coste and Romberg Model G gravity meters. Corrections for meter calibration, solar and lunar tides, instrument drift, station latitude, and elevation were made by the computer program GRAVPAC (LaCoste and Romberg, 1989). The resulting Bouguer gravity anomalies were examined for suspect data. Questionable data were removed. Strong regional components to the gravity field necessitated the use of filtering methods. These methods included using published data, upward continuation, and wavelength filtering. The upward continuation and. wavelength filtering were performed using the computer program FFTFIL (Hildenbrand, 1983). Both the published data and the upward continuation methods produced reasonable regional anomaly patterns, but difficulties were encountered when attempting to remove the regional field from the Bouguer gravity anomalies. The wavelength filtering method yielded satisfactory results using a filter window of 1.5 km to 10 km. The regional field was compared. With structure contour maps produced from deep oil well data to ensure that an appropriate field had been removed. A three-dimensional computer modelling program was written to simulate the observed gravity anomalies. Forward modelling was then performed by adjusting density contrast, depth and thickness parameters. Shallow water well data were used to establish initial model parameters. The modelling generated reasonable results which made it possible to infer probable channel locations, depths, and thicknesses. The major limitations of the computer modelling were lengthy processing times and limited geologic data. The filtered gravity signals show several discernible low anomaly patterns which are interpreted to be stream channel aquifers. Aquifers with significant density contrasts (\u3e0.2 g/cm3) and sufficient areal extent and thicknesses were located by this method

Geophysical investigation and assessment of the Rye Patch Known Geothermal Resource Area, Rye Patch, Nevada

A gravity and ground-based magnetic survey was conducted at the Rye Patch Known Geothermal Resource Area located at Rye Patch, Nevada. The purpose of the study was to attempt to further delineate the geothermal reservoir and/or to identify potential drilling targets. The survey consisted of collecting data at 264 new stations to augment data from 203 stations collected in 2008. Information from previous seismic, aeromagnetic and geochemical investigations was also examined and incorporated. Filtering methods including removal of a polynomial trend surface and wavelength filtering were utilized on the gravity data to remove the strong regional overprint caused by the large density contrast between the low density alluvium within the valley versus the near-surface higher density rock in the higher elevations. After filtering, the Rye Patch Fault, the Range Front Fault, an eastwest trending feature at the location of “southeast” fault, and another possible fault at the southern end of the study area are observable in the Rye Patch geothermal anomaly area. In the Humboldt House anomaly area, the northeast trending features identified by MacNight et al. (2005) and Ellis (2011) are not discernable although there is a significant gravity low in this area. Based on estimates arrived at by using 2 derivative methods, fault dip angles are on the order of 80 and are nd oconsistent with previous conceptual models of the site. Computer modelingindicates that the fault blocks may also be rotated back to the east. Due to errors in collecting diurnal information, the ground-based magnetic information was of limited use. Anomalies identified with the magnetic data do however correlate with the locations of anomalies identified using gravity and aeromagnetic surveys. Results indicate that gravity methods can be an effective method of defining approximate fault locations, lengths, and approximate trends and dip angles