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451.
Software receivers have had a discernable impact on the GNSS research community. Often such receivers are implemented in a compiled programming language, such as C or C++. A software receiver must emulate the digital signal processing (DSP) algorithms executed on dedicated hardware in a traditional receiver. The DSP algorithms, most notably correlation, have a high computational cost; this burden precludes many software receivers from running in real time. However, the computational cost can be lessened by utilizing single instruction multiple data (SIMD) operations found on modern ×86 processors. The following demonstrates how C/C++ compatible code can be written to directly utilize the SIMD instructions. First, an analysis is carried out to demonstrate why real time operation is not possible when using traditional C/C++ code is carried out. Secondly a tutorial outlines how to write and insert ×86 assembly, with SIMD operations, into C/C++ code. Performance gains achieved via SIMD operations are then demonstrated, and pseudo code outlines how SIMD operations can be employed to perform correlation. Finally, a C/C++ compatible SIMD enabled arithmetic library is added to the GPS Toolbox for use in software receivers. 相似文献
452.
453.
When individual cells of a multiple-cell treatment wetland are hydraulically connected, the wetland has a cell-network structure. The hydraulic performance of treatment wetlands is often characterized using tracer residence time distributions (RTDs) measured between the wetland inlet and outlet, such that the wetland is considered as a single hydraulic unit, regardless of the extent of networking between individual internal cells. This work extends the single hydraulic unit approach to enable the specification of moments and RTD parameters for individual cells, or clusters of cells, within the cell-network based on inert tracer tests with injection only at the network inlet. Hydraulic performance is quantified in terms of hydraulic efficiency and travel time dimensionless variance using both the method of moments and RTD modeling. Cell-network analysis was applied to a case study from the Orlando Easterly Wetland (OEW), demonstrating the improvement in hydraulic performance of individual wetland cells following wetland restoration activities. Furthermore, cell-network analysis indicated that the location of water quality sampling station locations within the cell network can significantly affect the accuracy of pollutant removal effectiveness estimation when the individual sample station RTD does not represent the hydraulic unit RTD. At the OEW, it was determined that historical nutrient removal effectiveness estimation may be underestimated for one area and overestimated for another, and recommendations were provided for sample station locations to minimize future performance estimation errors. 相似文献
454.
Large phreatomagmatic vent complex at Coombs Hills, Antarctica: Wet, explosive initiation of flood basalt volcanism in the Ferrar-Karoo LIP 总被引:2,自引:2,他引:2
The Mawson Formation and correlatives in the Transantarctic Mountains and South Africa record an early eruption episode related
to the onset of Ferrar-Karoo flood basalt volcanism. Mawson Formation rocks at Coombs Hills comprise mainly (≥80% vol) structureless
tuff breccia and coarse lapilli tuff cut by irregular dikes and sills, within a large vent complex (>30 km2). Quenched juvenile fragments of generally low but variable vesicularity, accretionary lapilli and country rock clasts within
vent-fill, and pyroclastic density current deposits point to explosive interaction of basalt with groundwater in porous country
rock and wet vent filling debris. Metre-scale dikes and pods of coherent basalt in places merge imperceptibly into peperite
and then into surrounding breccia. Steeply dipping to sub-vertical depositional contacts juxtapose volcaniclastic rocks of
contrasting componentry and grainsize. These sub-vertical tuff breccia zones are inferred to have formed when jets of debris
+ steam + water passed through unconsolidated vent-filling deposits. These jets of debris may have sometimes breached the
surface to form subaerial tephra jets which fed subaerial pyroclastic density currents and fall deposits. Others, however,
probably died out within vent fill before reaching the surface, allowing mixing and recycling of clasts which never reached
the atmosphere. Most of the ejecta that did escape the debris-filled vents was rapidly recycled as vents broadened via lateral
quarrying of country rock and bedded pyroclastic vent-rim deposits, which collapsed along the margins into individual vents.
The unstratified, poorly sorted deposits comprising most of the complex are capped by tuff, lapilli tuff and tuff breccia
beds inferred to have been deposited on the floor of the vent complex by pyroclastic density currents. Development of the
extensive Coombs Hills vent-complex involved interaction of large volumes of magma and water. We infer that recycling of water,
as well as recycling of pyroclasts, was important in maintaining water supply for phreatomagmatic interactions even when aquifer
rock in the vent walls lay far from eruption sites as a consequence of vent-complex widening. The proportion of recycled water
increased with vent-complex size in the same way that the proportion of recycled tephra did. Though water recycling leaves
no direct rock record, the volcaniclastic deposits within the vent complex show through their lithofacies/structural architecture,
lithofacies characteristics, and particle properties clear evidence for extensive and varied recycling of material as the
complex evolved.
Editorial responsibility: J. Donnelly-Nolan 相似文献
455.
Steven L. Morey Mark A. Bourassa Dmitry S. Dukhovskoy James J. O’Brien 《Ocean Dynamics》2006,56(5-6):594-606
A coupled ocean and boundary layer flux numerical modeling system is used to study the upper ocean response to surface heat
and momentum fluxes associated with a major hurricane, namely, Hurricane Dennis (July 2005) in the Gulf of Mexico. A suite
of experiments is run using this modeling system, constructed by coupling a Navy Coastal Ocean Model simulation of the Gulf
of Mexico to an atmospheric flux model. The modeling system is forced by wind fields produced from satellite scatterometer
and atmospheric model wind data, and by numerical weather prediction air temperature data. The experiments are initialized
from a data assimilative hindcast model run and then forced by surface fluxes with no assimilation for the time during which
Hurricane Dennis impacted the region. Four experiments are run to aid in the analysis: one is forced by heat and momentum
fluxes, one by only momentum fluxes, one by only heat fluxes, and one with no surface forcing. An equation describing the
change in the upper ocean hurricane heat potential due to the storm is developed. Analysis of the model results show that
surface heat fluxes are primarily responsible for widespread reduction (0.5°–1.5°C) of sea surface temperature over the inner
West Florida Shelf 100–300 km away from the storm center. Momentum fluxes are responsible for stronger surface cooling (2°C)
near the center of the storm. The upper ocean heat loss near the storm center of more than 200 MJ/m2 is primarily due to the vertical flux of thermal energy between the surface layer and deep ocean. Heat loss to the atmosphere
during the storm’s passage is approximately 100–150 MJ/m2. The upper ocean cooling is enhanced where the preexisting mixed layer is shallow, e.g., within a cyclonic circulation feature,
although the heat flux to the atmosphere in these locations is markedly reduced. 相似文献
456.
Dorothy L. Parker Takami Morita Rebecca Verity James K. McCarthy 《Geochimica et cosmochimica acta》2007,71(23):5672-5683
To examine the pathways that form Mn(III) and Mn(IV) in the Mn(II)-oxidizing bacterial strains Pseudomonas putida GB-1 and MnB1, and to test whether the siderophore pyoverdine (PVD) inhibits Mn(IV)O2 formation, cultures were subjected to various protocols at known concentrations of iron and PVD. Depending on growth conditions, P. putida produced one of two oxidized Mn species - either soluble PVD-Mn(III) complex or insoluble Mn(IV)O2 minerals - but not both simultaneously. PVD-Mn(III) was present, and MnO2 precipitation was inhibited, both in iron-limited cultures that had synthesized 26-50 μM PVD and in iron-replete (non-PVD-producing) cultures that were supplemented with 10-550 μM purified PVD. PVD-Mn(III) arose by predominantly ligand-mediated air oxidation of Mn(II) in the presence of PVD, based on the following evidence: (a) yields and rates of this reaction were similar in sterile media and in cultures, and (b) GB-1 mutants deficient in enzymatic Mn oxidation produced PVD-Mn(III) as efficiently as wild type. Only wild type, however, could degrade PVD-Mn(III), a process linked to the production of both MnO2 and an altered PVD with absorbance and fluorescence spectra markedly different from those of either PVD or PVD-Mn(III). Two conditions, the presence of bioavailable iron and the absence of PVD at concentrations exceeding those of Mn, both had to be satisfied for MnO2 to appear. These results suggest that P. putida cultures produce soluble Mn(III) or MnO2 by different and mutually inhibitory pathways: enzymatic catalysis yielding MnO2 under iron sufficiency or PVD-promoted oxidation yielding PVD-Mn(III) under iron limitation. Since PVD-producing Pseudomonas species are environmentally prevalent Mn oxidizers, these data predict influences of iron (via PVD-Mn(III) versus MnO2) on the global oxidation/reduction cycling of various pollutants, recalcitrant organic matter, and elements such as C, S, N, Cr, U, and Mn. 相似文献
457.
Yousif K. Kharaka Evangelos Kakouros James J. Thordsen Gil Ambats Marvin M. Abbott 《Applied Geochemistry》2007
For the last 5 a, the authors have been investigating the transport, fate, natural attenuation and ecosystem impacts of inorganic and organic compounds in releases of produced water and associated hydrocarbons at the Osage-Skiatook Petroleum Environmental Research (OSPER) “A” and “B” sites, located in NE Oklahoma. Approximately 1.0 ha of land at OSPER “B”, located within the active Branstetter lease, is visibly affected by salt scarring, tree kills, soil salinization, and brine and petroleum contamination. Site “B” includes an active production tank battery and adjacent large brine pit, two injection well sites, one with an adjacent small pit, and an abandoned brine pit and tank battery site. Oil production in this lease started in 1938, and currently there are 10 wells that produce 0.2–0.5 m3/d (1–3 bbl/d) oil, and 8–16 m3/d (50–100 bbl/d) brine. Geochemical data from nearby oil wells show that the produced water source is a Na–Ca–Cl brine (∼150,000 mg/L TDS), with high Mg, but low SO4 and dissolved organic concentrations. Groundwater impacts are being investigated by detailed chemical analyses of water from repeated sampling of 41 boreholes, 1–71 m deep. The most important results at OSPER “B” are: (1) significant amounts of produced water from the two active brine pits percolate into the surficial rocks and flow towards the adjacent Skiatook reservoir, but only minor amounts of liquid petroleum leave the brine pits; (2) produced-water brine and minor dissolved organics have penetrated the thick (3–7 m) shale and siltstone units resulting in the formation of three interconnected plumes of high-salinity water (5000–30,000 mg/L TDS) that extend towards the Skiatook reservoir from the two active and one abandoned brine pits; and (3) groundwater from the deep section of only one well, BR-01 located 330 m upslope and west of the site, appear not to be impacted by petroleum operations. 相似文献
458.
Al James 《Geoforum》2007,38(2):393-413
In recent years, economic geographers have drawn extensively upon notions of ‘cultural embeddedness’ to explore how spatially variable sets of cultural conventions, norms, values and beliefs shape firms’ innovative performance in dynamic regional economies. However, our understanding of these causal links remains partial, reinforced by an ‘over-territorialised’ conception of cultural embeddedness which sidelines the role of institutional actors operating outside and across the boundaries of ‘the local’. So motivated, this paper offers a theoretically-informed - and theoretically informing - empirical analysis of the high tech regional economy in Salt Lake City, Utah to explore the everyday causal mechanisms, practices and processes - both local and extra-local - through which firms’ cultural embedding within the region is manifested, performed and (un)intentionally (re)produced. In so doing, this paper aims to further our understanding of the constitutive entanglement and complex interweaving of cultural/economic practices, and to contribute to the development of an in-depth empirical corpus of work which compliments the exciting conceptual developments that have largely dominated cultural economic geography over the last decade. 相似文献
459.
Leon Bagas David L. Huston James Anderson Terrence P. Mernagh 《Mineralium Deposita》2007,42(1-2):127-144
Significant gold deposits in the western Tanami region of Western Australia include deposits in the Bald Hill and Coyote areas. The ca. 1,864 Ma Bald Hill sequence of turbiditic and mafic volcanic rocks hosts the Kookaburra and Sandpiper deposits and a number of smaller prospects. The ca. 1,835 Ma turbiditic Killi Killi Formation hosts the Coyote deposit and several nearby prospects. The Kookaburra deposit forms as a saddle reef within a syncline, and the Sandpiper deposit is localized within graphitic metasedimentary rocks along a limb of an anticline. Gold in these deposits is hosted by anastomosing quartz–(–pyrite–arsenopyrite) veins within quartz–sericite schist with disseminated arsenopyrite, pyrite, and marcasite (after pyrrhotite). Based on relative timing relationships with structural elements, the auriferous veins are interpreted to have been emplaced before or during the ca. 1,835–1,825 Ma Tanami Orogeny (regional D1). Gold deposition is thought to have been caused by pressure drops associated with saddle reef formation (Kookaburra) and chemical reactions with graphitic rocks (Sandpiper). The Coyote deposit, the largest in the western Tanami region, consists of a number of ore lenses localized along the limbs of the Coyote Anticline, which formed during the Tanami Orogeny. The largest lenses are associated with the Gonzalez Fault, which is located along the steeply dipping southern limb of this fold. Gold was introduced at ca. 1,790 Ma into dilatant zones that formed in local perturbations along this fault during later reactivation (regional D5) towards the end of a period of granite emplacement. Gold is associated with quartz–chlorite–pyrite–(arsenopyrite–galena–sphalerite) veins with narrow (<?5 mm) chloritic selvages. A quartz–muscovite–biotite–K–feldspar–(tourmaline–actinolite–arsenopyrite) assemblage, which is interpreted to relate to granite emplacement, overprints the regional greenschist facies metamorphic assemblage. The mineralogical similarity between this overprinting assemblage and the vein assemblage suggests that the auriferous veins at the Coyote deposit are associated with the granite-related metamorphic–metasomatic assemblage. Gold deposition is thought to have been caused by pressure drops within dilatant zones. 相似文献
460.
Michael C. Murrell James D. Hagy Emile M. Lores Richard M. Greene 《Estuaries and Coasts》2007,30(3):390-402
The relationships between phytoplankton productivity, nutrient distributions, and freshwater flow were examined in a seasonal
study conducted in Escambia Bay, Florida, USA, located in the northeastern Gulf of Mexico. Five sites oriented along the salinity
gradient were sampled 24 times over the 28-mo period from 1999 to 2001. Water column profiles of temperature and salinity
were measured along with surface chlorophyll and surface inorganic nutrient concentrations. Primary productivity was measured
at 2 sites on 11 dates, and estimated for the remaining dates and sites using an empirical regression model relating phytoplankton
net production to the product of chlorophyll, euphotic zone depth, and daily solar insolation. Freshwater flow into the system
varied markedly over the study period with record low flow during 2000, a flood event in March 2001, and subsequent resumption
of normal flow. Flushing times ranged from 1 d during the flood to 20 d during the drought. Freshwater input strongly affected
surface salinity distributions, nutrient flux, chlorophyll, and primary productivity. The flood caused high turbidity and
rapid flushing, severely reducing phytoplankton production and biomass accumulation. Following the flood, phytoplankton biomass
and productivity sharply increased. Analysis of nutrient distributions suggested Escambia Bay phytoplankton alternated between
phosphorus limitation during normal flow and nitrogen limitation during low flow periods. This study found that Escambia Bay
is a moderately productive estuary, with an average annual integrated phytoplankton production rate of 290 g C m−2 yr−1. 相似文献