Late superhumps and the stream–disc impact in IY UMa     

Daniel J. Rolfe  Carole A. Haswell  Joseph Patterson 《Monthly notices of the Royal Astronomical Society》2001,324(3):529-536

We present two simple dynamical models for Sagittarius based on N -body simulations of the progressive disruption of a satellite galaxy orbiting for 12.5 Gyr within a realistic Galactic potential. In both models the satellite initially has observable properties similar to those of current outlying dwarfs; in one case it is purely stellar while in the other it is embedded in an extended massive halo. The purely stellar progenitor is a King model with a total velocity dispersion of 18.9 km s⁻¹, a core radius of 0.44 kpc and a tidal radius of 3 kpc. The initial stellar distribution in the other case follows a King profile with the same core radius, a slightly larger total velocity dispersion and similar extent. Both these models are consistent with all published data on the current Sagittarius system, they match not only the observed properties of the main body of Sagittarius, but also those reported for unbound debris at larger distances.  相似文献   

Estimation of Biodegradation Rates Using Respiration Tests During In Situ Bioremediation of Weathered Diesel NAPL   总被引：3，自引：1，他引：2  

G.B. Davis  C.D. Johnston  B.M. Patterson  C. Barber  M. Bennett 《Ground Water Monitoring & Remediation》1998,18(2):123-132

Respiration tests were carried out during a seven month bioremediation field trial to monitor biodegradation rates of weathered diesel non-aqueous phase liquid (NAPL) contaminating a shallow sand aquifer. Multiple depth monitoring of oxygen concentrations and air-filled porosity were carried out in nutrient amended and nonamended locations to assess the variability of degradation rate estimates calculated from respiration tests.
The field trial consisted of periodic addition of nutrients (nitrogen and phosphorus) and aeration of a 100 m² trial plot. During the bioremediation trial, aeration was stopped periodically, and decreases in gaseous oxygen concentrations were logged semi-continuously using data loggers attached to recently developed in situ oxygen probes placed at multiple depths above and within a thin NAPL-contaminated zone. Oxygen usage rate coefficients were determined by fitting zero-and first-order rate equations to the oxygen concentration reduction curves, although only zero-order rates were used to calculate biodegradation rates. Air-filled porosity estimates were found to vary by up to a factor of two between sites and at different times.
NAPL degradation rates calculated from measured air-filled porosity and oxygen usage rate coefficients ranged up to 69 mg kg^-1 day^-1. These rates are comparable to and higher than rates quoted in other studies, despite the high concentrations and weathered state of the NAPL at this test site. For nutrient-amended sites within the trial plot, estimates of NAPL degradation rates were two to three times higher than estimates from nonamended sites. Rates also increased with depth.  相似文献   

Preservation of extraterrestrial 3He in 480-Ma-old marine limestones.   总被引：3，自引：0，他引：3  

D B Patterson  K A Farley  B Schmitz 《Earth and Planetary Science Letters》1998,163(1-4):315-325

We have measured the helium abundance and isotopic composition of a suite of Lower Ordovician marine limestones and associated fossil meteorites from Kinnekulle, Sweden. Limestone 3He/4He ratios as high as 11.5 times the atmospheric value in fused samples and up to 23 times atmospheric in a single step-heat fraction indicate the presence of extraterrestrial helium, and demonstrate that at least a fraction of the extraterrestrial 3He carried by interplanetary dust particles must be retained against diffusive and diagenetic losses for up to 480 Ma. The carrier phase has not been identified but is not magnetic. Extrapolation of high-temperature 3He diffusivities in these sediments is consistent with strong retention of extraterrestrial 3He under ambient Earth-surface conditions. Combination of the observed helium concentrations with sedimentation rates estimated from conodont biostratigraphy suggest that the flux of extraterrestrial 3He in the Early Ordovician was about 0.5 x 10(-12) cm3 STP cm-2 ka-1, ignoring potential post-deposition helium loss. This value is indistinguishable from the average 3He flux estimated for the Cenozoic Era. In contrast, previous studies of fossil meteorites, Ir abundances, and Os isotopic ratios in the limestone suggest that the total accretion rate of extraterrestrial material during the studied interval was at least an order of magnitude higher than the Cenozoic average. This disparity may reflect significant post-depositional loss of 3He from IDPs within these old limestones; if so, the match between the Ordovician flux and the Cenozoic average would be fortuitous. Alternatively, the size distribution of infalling objects during the Early Ordovician may have been enriched only in extraterrestrial material too large to retain 3He during atmospheric entry heating (> approximately 30 micrometers). The fossil meteorites themselves also preserve extraterrestrial helium. Meteorite 3He concentrations of 2 to 9 x 10(-12) cm3 STP g-1 are several orders of magnitude lower than found in most modern meteorites, suggesting very substantial helium loss (probably >99.9%) from these chemically altered objects. The Meteorites carry 3He concentrations only a factor of a few higher than the host limestones. The meteorites themselves cannot be the source of the extraterrestrial 3He observed in the limestones.  相似文献   

Book reviews     

John A. Patterson  Janet S. Sachs 《Natural Resources Research》1998,7(1):85-86

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"An empire lost but a province gained": a cohort analysis of British international retirement in the Algarve     

Williams AM  Patterson G 《International journal of population geography : IJPG》1998,4(2):135-155

"The growth of international retirement in the Algarve has coincided with a number of changes in the international framework for population mobility as well as in the nature of the Algarve [Portugal] as a destination area. Tourism development, which is intimately linked to subsequent retirement migration, is particularly important in this. This paper considers the nature of the link between cycles of migration and of development in recipient areas, in the context of the remarkable and relatively late development of the Algarve as an area of tourism and retirement.... Cohort analysis...provides the basis for an examination of changes over time in the socio-demographic profiles of the migrants, their motivations, their residential patterns and their integration."  相似文献   

The SU Ursae Majoris Star TU Crateris     

R.E. Mennickent  J. Patterson  D. O'Donoghue  E. Unda  D. Harvey  T. Vanmuster  G. Bolt 《Astrophysics and Space Science》1998,262(1):1-13

We have established that the cataclysmic variable TU Crateris is an SU UMa star. Superhumps were observed after 3 days of the 1998 March-April supermaximum, repeating with a mean period of P_s = 0d.08535(5). Timings of superhump maxima revealed a period decrease of P = 7.2 × 10^-5. Based on an empirical relationship, we estimated an orbital period of 0d.0810(25), just in the lower limit of the reported quiescence photometric period. H emission lines during quiescence vary with the orbital period with radial velocity half amplitude of 70 ± 19 km s^-1, evidencing a hotspot located in front of the standard position.  相似文献   

Erratum to: Influence of ocean–atmospheric oscillations on lake ice phenology in eastern North America     

R. Timothy Patterson  Graeme T. Swindles 《Climate Dynamics》2015,45(9-10):2963-2963

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Relationship between ecological indicators (Arcellacea), total mercury concentrations and grain size in lakes within the Athabasca oil sands region,Alberta     

L. A. Neville  R. T. Patterson  P. Gammon  A. L. Macumber 《Environmental Earth Sciences》2014,72(2):577-588

Industrial mercury (Hg) sources associated with the processing of Athabasca oil sands (AOS), Alberta, Canada, may pose an environmental risk to nearby water bodies via either waterborne or airborne transport. Using a dataset derived from 63 lakes in the area, this study investigates the relationships between total-Hg (THg), organic matter, grain size, and lake ecology as measured by environmentally sensitive arcellacean (testate lobose amoebae) communities. The lakes studied include 59 lakes within a 75 km radius of the operations, plus four distal lakes ~150 km from the main industrial operations. Hg transport to the lakes is primarily through airborne pathways. The four distal lakes in the Peace–Athabasca Delta (~150 km downstream of the AOS operations) were examined to determine if the operation is emitting potential waterborne inputs, in addition to airborne inputs, and to identify any associated impact to those ecosystems. Total mercury in lakes close to the AOS were similar to values recorded in lakes farthest away. THg was most closely linked to the silt fraction, suggesting much of the Hg in these lakes is minerogenic in origin, either adsorbed and/or lattice-bound. THg is not statistically related to organic matter as has been observed in other Canadian lakes. The ecologic response to THg levels was investigated via the distribution of key indicator species and, or species diversity (Shannon diversity index). The spatial extent of arcellacean ecosystem stress in the study lakes did not correlate with THg concentrations. This is perhaps due to the generally low THg levels found in these lakes, all except one had THg concentrations lower than current CCME guidelines. While these findings may rule out any direct link between THg concentrations in the lakes and observed Arcellacea faunas, ecosystem stress unrelated to THg was observed northeast of the AOS, which warrants further examination. The results of this research suggest that the natural lake arcellacean faunas in the region are not being significantly impacted by current THg concentrations.  相似文献   

Geochemical controls on sediment reactivity and buffering processes in a heterogeneous aquifer     

Carlos Descourvières  Niels Hartog  Bradley M. Patterson  Carolyn Oldham  Henning Prommer 《Applied Geochemistry》2010

The injection and recovery of oxic water into deep anoxic aquifers may help to alleviate short- and long-term imbalance between freshwater supply and demand. The extent and structure of physical and geochemical heterogeneity of the aquifer will impact the water quality evolution during injection, storage and recovery. Water–sediment interactions within the most permeable parts of the aquifer, where the bulk of the injectant will penetrate, may dominate, however, water quality may also be impacted by interactions within the finer-grained, less permeable but potentially highly reactive media. In this study, the heterogeneity of the reductive capacity of an aquifer selected for water reuse projects was characterised, the amount, type and reactivity of the sedimentary reductants present determined, and the relationship between reductive capacity and sedimentary lithologies quantified. The average potential reductive capacities (PRC_TOT), based on total organic C and pyrite concentrations of the sediment, were quantified for sands (382 μmol O₂ g⁻¹), clays (1522 μmol O₂ g⁻¹), and silts (1957 μmol O₂ g⁻¹). Twenty-seven samples, spanning the three different lithologies, were then incubated for 50 days and the measured reductive capacities (MRC) determined for the sands (29.2 μmol O₂ g⁻¹), silts (136 μmol O₂ g⁻¹), and clays (143 μmol O₂ g⁻¹). On average, the MRC were 10% of the PRC_TOT. The main consumers of O₂ were pyrite (20–100%), sedimentary organic matter (SOM; 3–56%), siderite (3–28%) and Fe(II)-aluminosilicates (8–55%). The incubation data plus hydrogeochemical modelling, indicated that pH-buffering was controlled firstly by dissolution of trace level carbonates, followed by dissolution of feldspars. Zinc, Co, Ni, Cd and Pb were readily mobilized during incubation.  相似文献   

Patterns in the local assembly of Egyptian rodent faunas: Co-occurrence and nestedness     

M. Abu Baker  B.D. Patterson 《Journal of Arid Environments》2011,75(1):14-19

We studied co-occurrence patterns of 29 rodents across 308 sites in Egypt to evaluate spatial variation and non-randomness in community assembly (co-occurrence and nestedness). There was strong evidence for negative species association in the entire fauna. Negative associations can be traced to habitat segregation among species, the discreteness of habitats, low species richness at local assemblages due to aridity and low primary productivity, and allopatry of sibling species. Nevertheless, high degree of nestedness characterizes the entire collection, as tested by BINMATNEST and Aninhado. Species ranks in the packed matrix were significantly correlated with incidence, total abundance, number of coexisting species, total number of species combinations, and range size. Analyses of the assemblages by region and sampling intensity using Aninhado simulations confirmed the nestedness for the whole fauna and showed little or no nested structure in species incidences.Egyptian rodent faunas appear to be structured by a dynamic interplay of biotic and abiotic factors operating on distinct sets of species with shared habitat preferences and requirements. Local assembly patterns may result from interspecific interactions coupled with aridity and low productivity, habitat requirements, and historical factors. The harsh conditions of these arid regions led to the prevalence of species exclusion.  相似文献