An investigation of GNSS atomic clock behavior at short time intervals     

Erin Griggs  E. Robert Kursinski  Dennis Akos 《GPS Solutions》2014,18(3):443-452

A technique for obtaining clock measurements from individual GNSS satellites at short time intervals is presented. The methodology developed in this study allows for accurate satellite clock stability analysis without an ultra-stable clock at the ground receiver. Variations in the carrier phase caused by the satellite clock are isolated using a combination of common GNSS carrier-phase processing techniques. Furthermore, the white phase variations caused by the thermal noise of the collection and processing equipment are statistically modeled and removed, allowing for analysis of clock performance at subsecond intervals. Allan deviation analyses of signals collected from GPS and GLONASS satellites reveal distinct intervals of clock noise for timescales less than 100 s. The clock data collected from GPS Block IIA, IIR, IIR-M, and GLONASS satellites reveal similar stability performance at time periods greater than 20 s. The GLONASS clock stability in the 0.6–10 s range, however, is significantly worse than GPS. Applications that rely on ultra-stable clock behavior from the GLONASS satellites at these timescales may therefore require high-rate corrections to estimate and remove oscillator-based errors in the carrier phase.  相似文献   

Thermal modeling of shock melts in Martian meteorites: Implications for preserving Martian atmospheric signatures and crystallization of high‐pressure minerals from shock melts     

Cliff S. J. Shaw  Erin Walton 《Meteoritics & planetary science》2013,48(5):758-770

The distribution of shock melts in four shergottites, having both vein and pocket geometry, has been defined and the conductive cooling time over the range 2500 °C to 900 °C calculated. Isolated 1 mm² pockets cool in 1.17 s and cooling times increase with pocket area. An isolated vein 1 × 7 mm in Northwest Africa (NWA) 4797 cools to 900 °C in 4.5 s. Interference between thermal haloes of closely spaced shock melts decreases the thermal gradient, extending cooling times by a factor of 1.4 to 100. This is long enough to allow differential diffusion of Ar and Xe from the melt. Small pockets (1 mm²) lose 2.2% Ar and 5.2% Xe during cooling, resulting in a small change in the Ar/Xe ratio of the dissolved gas over that originally trapped. With longer cooling times there is significant fractionation of Xe from Ar and the Ar/Xe ratio increases rapidly. The largest pockets show less variation of Ar/Xe and likely preserve the original trapped gas composition. Considering all of the model calculations, even the smallest isolated pockets have cooling times greater than the duration of the pressure pulse, i.e., >0.01 s. The crystallization products of these shock melts will be unrelated to the peak shock pressure experienced by the meteorite.  相似文献   

The use of passive treatment alternatives for the mitigation of acidic drainage at the Williams Brother mine,California: Bench-scale study     

Erin J. Clyde  Pascale Champagne  Heather E. Jamieson 《Applied Geochemistry》2010

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Relationships between phytoplankton standing crop and physical, chemical, and biological gradients in the Suwannee River and plume region, U.S.A.     

Erin L. Bledsoe  Edward J. Phlips 《Estuaries and Coasts》2000,23(4):458-473

The Suwannee River (USA) is an amber stained, nutrient rich, blackwater river which flows into relatively clear oceanic waters resulting in the formation of a coastal region with unique physical, chemical, and biological gradients. The intent of this study was to describe the spatial and temporal variability of phytoplankton as it relates to these gradients. Ten stations along a transect ranging from 5 km up river to 31 km offshore, were sampled during four different flow regimes. All four sampling periods included in our study of the Suwannee River and plume region exhibited a similar pattern of phytoplankton abundance; low phytoplankton biomass in the Suwannee River and offshore stations with an area of elevated biomass seaward of the Suwannee River outflow. The results of our analysis of light and nutrient limitation in the region support the hypothesis that this spatial pattern of phytoplankton abundance is strongly influenced by color dependent light limitation in the river and outflow area, combined with nutrient limitation offshore. Our results suggest that both light and nutrient availability control abundance and composition of phyto plankton in this coastal area.  相似文献   

Rapid movement of wastewater from on-site disposal systems into surface waters in the Lower Florida Keys     

John H. Paul  Molly R. McLaughlin  Dale W. Griffin  Erin K. Lipp  Rodger Stokes  Joan B. Rose 《Estuaries and Coasts》2000,23(5):662-668

Viral tracer studies have been used previously to study the potential for wastewater contamination of surface marine waters in the Upper and Middle Florida Keys. Two bacteriophages, the marine bacteriophage ϕHSIC and theSalmonella phage PRD1, were used as tracers in injection well and septic tank studies in Saddlebunch Keys of the Lower Florida Keys and in septic tank studies in Boot Key Harbor, Marathon, of the Middle Keys. In Boot Key Harbor, both phages were detected in a canal adjacent to the seeded septic tank within 3 h 15 min of the end of the seed period. The tracer was then detected at all sampling sites in Boot Key Harbor, including one on the opposite side of U.S. Highway 1 in Florida Bay, and at an Atlantic Ocean beach outside Boot Key Harbor. Rates of migration based on first appearance of the phage ranged from 1.7 to 57.5 m h⁻¹. In Saddlebunch Keys, ϕHSIC and PRD1 were used to seed a residential septic tank and a commercial injection well. The septic tank tracer was not found in any surface water samples. The injection well tracer was first detected at a site most distant from the seed site, a channel that connected Sugarloaf Sound with the Atlantic Ocean. The, rate of tracer migration from the injection well to this channel ranged from 66.8 to 141 m h⁻¹. Both tracer studies showed a rapid movement of wastewater from on-site sewage treatment and disposal systems in a southeasterly direction toward the reef tract and Atlantic Ocean, with preferential movement through tidal channels. These studies indicate that wastewater disposal systems currently in widespread use in the Florida Keys can rapidly contaminate the marine environment.  相似文献   

Bioaugmentation in a Well‐Characterized Fractured Rock DNAPL Source Area          下载免费PDF全文

Charles E. Schaefer  Graig M. Lavorgna  Erin B. White  Michael D. Annable 《Ground Water Monitoring & Remediation》2017,37(2):35-42

A field demonstration was performed at Edwards Air Force Base to assess bioaugmentation for treatment of a well‐characterized tetrachloroethene (PCE) dense nonaqueous phase liquid (DNAPL) source area in fractured rock. Groundwater recirculation was employed to deliver remedial amendments, including bacteria, to facilitate reductive dechlorination and enhance DNAPL dissolution. An active treatment period of 9 months was followed by a 10‐month posttreatment rebound evaluation. Dechlorination daughter products were observed in both the shallow and deep fracture zones following treatment. In the shallow fracture zone, the calculated DNAPL mass removed was approximately equal to the DNAPL mass estimated using partitioning tracer testing, and no rebound in chlorinated ethenes or ethene was observed during the posttreatment period. A maximum DNAPL dissolution enhancement factor of 5 was observed in the shallow fracture zone. In the deep fracture zone, only approximately 45% of the DNAPL mass—as estimated via partitioning tracer testing—was removed and rebound in the total molar chlorinated ethenes + ethene was observed. The difference in behavior between the shallow and deep fracture zones was attributed to DNAPL architecture and the fracture flow field.  相似文献   

From Lightning Rod to Community Asset? The Creation of a Protected Area in Northern California and its Evolving Relationship to a Nearby Community     

Erin Clover Kelly  Alicia Christiansen 《社会与自然资源》2019,32(6):657-674

Researchers have described shifting relationships between communities and Protected Areas (PAs), from excluding communities to consultative relationships to participatory models. This research focuses on a PA created on formerly industrial timberland that was the focus of conflict between environmental activists and the timber industry. In a nearby formerly timber-dependent community, we assessed community use and support of the PA, and its perceived purposes and benefits, through a survey of residents and interviews with key stakeholders. Despite intense conflict surrounding its creation, we found support for the PA, and our case suggests a new possible relationship between PAs and communities, which is mitigating and helping to resolve natural resource conflict. We also found that community well-being benefits of the PA were unclear; we suggest that PA management should include cultural, economic, and historical context in objectives and interpretive materials; and should work to create economic opportunities connected to the PA.  相似文献   

Variation in groundwater salinity in a tidal salt marsh basin,North Inlet Estuary,South Carolina     

Erin S. Carter  Scott M. White  Alicia M. Wilson 《Estuarine, Coastal and Shelf Science》2008

Groundwater flow of freshwater from upland forests into salt marshes is influenced by hydrologic forces that operate over a wide range of temporal scales, including storm events, tidal fluctuations, seasonal variations in rainfall and evapotranspiration (ET). Groundwater salinity can be a useful first order indicator of the balance between these flow processes. A dipole-dipole electrical resistivity survey was conducted approximately monthly during 2005 to measure groundwater salinity across a portion of Crabhaul Creek, a tidal salt marsh basin at the boundary of the upland forest and the North Inlet marsh in South Carolina. The monthly electrical resistivity surveys were designed to provide a detailed, spatially continuous measurement of subsurface conductivity to a depth of 4 m in order to further investigate the seasonal variation in groundwater salinity. Resistivity models were corroborated by simultaneous measurements of salinity in nearby piezometers. The freshwater-brackish water interface was clearly imaged by the resistivity. Movement of this interface occurs on a timescale of months rather than a regular seasonal variation. The average salinity in the marsh basin is highest in late Summer (July–August) when ET is highest, and lowest during the Winter (November–December). The position of the brackish-freshwater interface changes, but is not well correlated to local rainfall or tidal cycles except under specific circumstances. A steady-state hydrological model correctly predicts the average position of the freshwater-brackish interface and suggests a linear relationship between the height of the water table and the location of the interface. These results suggest a complex relationship between precipitation events and groundwater flow from the forest into the marsh.  相似文献