Space Rockets, Polar Bears, and Tundra Buggies – And a GPS Link to the Seventeenth Century     

David Underwood 《GPS Solutions》1999,3(2):48-52

The use of the Global Positioning System (GPS) for position and attitude determination has been exploited for many years. In these systems, it was required that multiple antennas maintained phase lock to common view satellites for long periods of time in order to determine integer ambiguities. The challenge to overcome with the ballistic space probe is the high rotational spin of this particular rocket. The antennas, mounted on the outside skin of the rocket, are in full view of each satellite only for a fraction of a second before the rocket core eclipses them as it rotates. The antennas rarely see common satellites. This article describes as system that overcomes these obstacles and provides position, acceleration, attitude, and rotation rate. The approach uses a two-antenna system. One antenna is mounted either side of the rocket facing out. A hybrid tracking channel combines signals from both antennas to overcome the signal blockage due to the rocket core as well as to defeat the effect on the tracking channel due to the spin. The amplitude and phase of the spin rotation signature from each satellite is extracted from the dual antenna data and used to compute the attitude and spin rate of the vehicle. ? 1999 John Wiley & Sons, Inc.  相似文献   

Variations of the Nutrients Loads to the Mainland U.K. Estuaries: Correlation with Catchment Areas, Urbanization and Coastal Eutrophication     

D. B. Nedwell  L. F. Dong  A. Sage  G. J. C. Underwood 《Estuarine, Coastal and Shelf Science》2002,54(6):951

The annual loads of nutrients (TO_xN equal to nitrate+nitrite; ammonium, phosphate, silicate) to all the estuaries on the mainland of the United Kingdom were estimated from data on water flow through gauging stations at the tidal limits of estuaries, and from concentration measurements under the Harmonised Monitoring Scheme of nutrient concentrations in water samples from these stations. The annual loads of nutrients showed distinct regional variations, with estuaries along the west coast of Wales and northern Scotland having much smaller loads than those along the east coast of England. The largest nitrogen loads were of TO_xN, and ammonium loads were usually small in comparison. The Severn, Mersey, Humber and Thames had the highest loads, although these were small in relation to the larger continental European estuaries. Loads of TO_xN per unit of catchment area were surprisingly constant (about 10⁵ moles N km⁻² y⁻¹). The nutrient loads showed that most U.K. catchments were influenced by human activity, the majority being in the ‘ moderately influenced ’ category. Nutrient loads were also normalized for the area of each estuary, as a measure of the relative influence of nutrients on the receiving estuaries. The ratios of N:P, N:Si and P:Si in the annual loads suggested that most estuaries were likely to be, if anything, P limited rather than N or Si limited. However, crude annual loads may conceal significant seasonal variations.The spring maximum chlorophylla concentrations in coastal waters adjacent to each estuary were significantly correlated with the log total annual loads of TO_xN, ammonium and phosphate (but not silicate) for each estuary, providing a direct link between a measure of the degree of biological response in coastal waters and the nutrient load through the estuaries. There were no significant correlations between spring maximum chlorophyll a concentrations and either catchment-normalized or estuary-normalized nutrient loads. There was significant correlation between catchment area-normalized loads of phosphate and an urbanization index for the catchments, but not with the catchment area-normalized loads of the other nutrients.  相似文献   

Chandra and XMM–Newton observations of NGC 4214: the hot interstellar medium and the luminosity function of dwarf starbursts     

Joanna M. Hartwell  Ian R. Stevens  David K. Strickland †  Timothy M. Heckman  Lesley K. Summers 《Monthly notices of the Royal Astronomical Society》2004,348(2):406-420

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Assessing the vulnerability of Australian skinks to climate change     

Abigail L. Cabrelli  Lesley Hughes 《Climatic change》2015,130(2):223-233

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Shark and ray faunas in the Middle and Late Eocene of the Fayum Area, Egypt     

Charlie J. Underwood  David J. Ward  Sameh M. Antar  Philip D. Gingerich 《Proceedings of the Geologists' Association. Geologists' Association》2011,122(1):47-66

The Eocene rocks exposed in the Fayum Area, Egypt, are well known for their fossil vertebrates but in recent times the sharks and rays have been largely neglected. Extensive surface collecting, supplemented with bulk samples, has produced large collections from the Midawara, Gehannam, Birket Qarun and Qasr el-Sagha formations, spanning the Bartonian and Priabonian stages and from palaeoenvironments varying from open muddy shelf to very shallow estuarine systems. In total about 90 species of sharks and rays are recorded, many of them previously unrecognised, resulting in some of the most diverse fossil chondrichthyan assemblages known from the Tertiary. Teeth of these species suggest that they occupied a wide range of ecological niches from top predator to tiny benthic invertebrate feeder to planktivore. Many of the species are limited in their stratigraphical range and show potential to be used, at least locally, as biostratigraphical indicators for stratigraphically poorly constrained vertebrate sites elsewhere in North Africa. Distinctly different faunas from different sedimentary environments indicate a strong environmental control on the distribution of many species.  相似文献   

Solid-phase considerations for the environmental fate of nitrobenzene and triazine munition constituents in soil     

Mark A. Chappell  Cynthia L. Price  Lesley F. Miller 《Applied Geochemistry》2011

This paper focuses on the chemistry of DoD-relevant organic contaminants in soil. Most of the work presented here is based on the author’s experience with the environmental fate of the munition constituents, TNT and RDX, for DoD related issues. The principles and challenges of understanding the transport of nitrobenzene and triazine compounds in the environment are captured. In this work, disparities in the current scientific literature with respect to the construction of sorption experiments are discussed, in terms of soil sample handling, dispersion state of the soil, and sorption hysteresis/equilibrium. Here is discussed the concept of environmentally formulated compounds and its implications toward reduced accuracy of predicting the environmental fate of munition constituents. Also, further research linking simple but oft-forgotten basic concepts of soil fertility to the transport and environmental fate of munition constituents are discussed.  相似文献   

Inter-annual variability of wet season freshwater plume extent into the Great Barrier Reef lagoon based on satellite coastal ocean colour observations     

Schroeder T  Devlin MJ  Brando VE  Dekker AG  Brodie JE  Clementson LA  McKinna L 《Marine pollution bulletin》2012,65(4-9):210-223

Riverine freshwater plumes are the major transport mechanism for nutrients, sediments and pollutants into the Great Barrier Reef (GBR) lagoon and connect the land with the receiving coastal and marine waters. Knowledge of the variability of the freshwater extent into the GBR lagoon is relevant for marine park management to develop strategies for improving ecosystem health and risk assessments. In this study, freshwater extent has been estimated for the entire GBR lagoon area from daily satellite observations of the Moderate Resolution Imaging Spectroradiometer (MODIS) between 2002 and 2010. To enable a reliable mapping of freshwater plumes we applied a physics-based coastal ocean colour algorithm, that simultaneously retrieves chlorophyll-a, non-algal particulate matter and coloured dissolved organic matter (CDOM), from which we used CDOM as a surrogate for salinity (S) for mapping the freshwater extent.  相似文献   

Uptake of palytoxin‐like compounds by shellfish fed Ostreopsis siamensis (Dinophyceae)     

Lesley Rhodes  Neale Towers  Lyn Briggs  Rex Munday  Janet Adamson 《新西兰海洋与淡水研究杂志》2013,47(3):631-636

Abstract

Greenshell? mussels (Perna canaliculus Gmelin), scallops (Pecten novaezealandiae Reeve), and Pacific oysters (Crassostrea gigas Thunberg) were fed with a New Zealand strain of mass cultured Ostreopsis siamensis Schmidt (for 27 and 84 h and with 1.5 × 10⁶ or 8.6 × 10⁶ cells, respectively) under laboratory conditions. The microalgal cells contained 0.3 pg palytoxin equivalents cell^–1 (as determined by the haemolysis neutralisation assay (HNA) of Bignami (1993)) and extracts of these cells were toxic to mice after intraperitoneal injection. No palytoxin‐like material was detected either in the hepatopancreas or the muscle and roe of mussels fed O. siamensis. Oysters contained detectable amounts of toxin in hepatopancreas muscle, and roe while higher concentrations were present in the hepatopancreas of scallops. Extracts of control shellfish (tested biotoxin free and not fed O. siamensis) were toxic to mice, and there was no definitive evidence that feeding shellfish with O. siamensis at the levels employed in the present experiment increased the toxicity of shellfish tissue extracts to mice.  相似文献   

Joint isotopic mass balance: a novel approach to quantifying channel bed to channel margins sediment transfer during storm events          下载免费PDF全文

John W. Underwood  Carl E. Renshaw  Francis J. Magilligan  W. Brian Dade  Joshua D. Landis 《地球表面变化过程与地形》2015,40(12):1563-1573

The important role of floodplains and the broader riparian zone in providing temporary storage for a large fraction of the annual sediment load of rivers is well established, but this understanding is largely based on observations of the long‐term average behavior of the catchment. Here we combine measurements of the fallout radionuclides ⁷Be and ²¹⁰Pb and the stable isotopes of hydrogen in water to quantify fine sediment mobilization and storage in a stream and its channel margins during individual intermediate‐sized storm events with recurrence intervals of a few months or less. We demonstrate this method using five storm events in a small (~15 km²), undeveloped, gravel‐bedded tributary of the Connecticut River (USA). We estimate that in each storm, the mass of sediment deposited onto the margins accounts for almost 90% of the sediment mobilized from the bed, with the remainder of the mobilized bed sediment transported downstream as suspended load. The result that the bed is a net source of sediment to the stream and the margins a net sink is robust, but estimates of the mass of material eroded from the bed and deposited on the margins are less certain. The source of sediment to the bed remains unclear as, consistent with earlier studies, we observe only limited deposition of sediment to the bed during the storm events. The suspended sediment is organic‐rich and thus its source may be associated with in‐channel organic decay between storm events. Understanding the coupled interactions between discharge magnitude and frequency and sediment resupply at the event time scale has important implications for stream restoration efforts seeking to connect the channel and the broader riparian zone, and for the development of accurate sediment budgets and predictions of sediment flux from a watershed. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

The hydrography and biology of a bloom of the coccolithophorid Emiliania huxleyi in the northern North Sea     

Robert N. Head  David W. Crawford  Jorun K. Egge  Roger P. Harris  Svein Kristiansen  David J. Lesley  Emilio Maran  David Pond  Duncan A. Purdie 《Journal of Sea Research》1998,39(3-4)

In June/July 1994 a study was made of a small bloom of the coccolithophorid Emiliania huxleyi in an area of the North Sea to the east of the Shetland Islands. Observations on the hydrography of the study area indicated the bloom was associated with Atlantic water and was confined to an area in which a stable shallow mixed layer had formed. There was no evidence to suggest association of horizontal physical structure with the bloom development. High cell densities of >1– cells dm⁻³, together with low concentrations of PIC (<50 μg dm⁻³) and detached liths (2– liths cm⁻³) indicated that the bloom was studied at an early stage of development. Biochemical and physiological observations indicated active growth was taking place. The results presented are discussed in comparison with previous studies carried out in both oceanic and shelf seas.  相似文献