冰穹C的大气条件:天文含意     

J.S. Lawrence　M.C.B. Ashley　M.G. Burton　J.W.V. Storey 《天文学报》2007,48(1):48-53

在南极洲高原的冰穹C有望发现非凡的天文观测条件,受此鼓舞,许多国际小组协同努力对该地的大气条件作全面的测量．评述对冰穹C的选址现况,讨论过去、现在和计划中的选址仪器,迄今已得到的结果,以及这些结果的天文含意．  相似文献   

Indirect effects of asymmetrical competition among top predators determine spatial patterns of predation risk for prey   总被引：1，自引：0，他引：1  

Angélique Dupuch  Andrea Bertolo  Pierre Magnan  Lawrence M. Dill 《Aquatic Sciences - Research Across Boundaries》2014,76(4):543-552

Asymmetrical interspecific competition among top predators can indirectly affect the predation risk for their prey by altering the abundance, diet, and habitat use of inferior competitors. However, the indirect effects of such biological interactions are poorly known because of the difficulties in measuring predation risk in nature. We addressed this issue by assessing the effect of asymmetrical competition among brook trout (Salvelinus fontinalis) and two superior non-piscivorous competitors, creek chub (Semotilus atromaculatus) and white sucker (Catostomus commersonii), on the predation risk of a brook trout prey, northern redbelly dace (Chrosomus eos). We determined the spatio-temporal patterns of relative predation risk of dace with tethering experiments in 11 lakes containing either only brook trout and dace (n = 5), or brook trout, dace, chub, and sucker (n = 6). The diel pattern of the relative predation risk and the overall relative predation risk of dace were not significantly different in lakes with or without brook trout competitors. However, we observed a significant shift in the relative predation risk from the lower pelagic to the upper pelagic and littoral zones in the presence of brook trout competitors. This study highlights the fact that the outcome of interactions can vary in space and that care should be used when extrapolating the results of small-scale experiments or coarse-scale estimates to the whole ecosystem.  相似文献   

Spitzer Space Telescope Infrared Spectrograph mapping of the central kpc of Centaurus A     

Alice C. Quillen  Joss Bland-Hawthorn  Joel D. Green  J. D. Smith  D. Amelia Prasad  Almudena Alonso-Herrero  Kieran Cleary  Mairi H. Brookes  Charles R. Lawrence 《Monthly notices of the Royal Astronomical Society》2008,384(4):1469-1482

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Principal Components and Independent Component Analysis of Solar and Space Data     

A.?C.?CadavidEmail author  J.?K.?Lawrence  A.?Ruzmaikin 《Solar physics》2008,248(2):247-261

Principal components analysis (PCA) and independent component analysis (ICA) are used to identify global patterns in solar and space data. PCA seeks orthogonal modes of the two-point correlation matrix constructed from a data set. It permits the identification of structures that remain coherent and correlated or that recur throughout a time series. ICA seeks for maximally independent modes and takes into account all order correlations of the data. We apply PCA to the interplanetary magnetic field polarity near 1 AU and to the 3.25R _⊙ source-surface fields in the solar corona. The rotations of the two-sector structures of these systems vary together to high accuracy during the active interval of solar cycle 23. We then use PCA and ICA to hunt for preferred longitudes in northern hemisphere Carrington maps of magnetic fields.  相似文献   

Metal tissue levels in Steller sea lion (Eumetopias jubatus) pups     

Holmes AL  Wise SS  Goertz CE  Dunn JL  Gulland FM  Gelatt T  Beckmen KB  Burek K  Atkinson S  Bozza M  Taylor R  Zheng T  Zhang Y  Aboueissa AM  Wise JP 《Marine pollution bulletin》2008,56(8):1416-1421

The endangered Western population of the Steller sea lion declined for three decades for uncertain reasons. We present baseline data of metal concentrations in pups as a first step towards investigating the potential threat of developmental exposures to contaminants. Seven metals were investigated: arsenic, cadmium, silver, aluminum, mercury, lead and vanadium. Vanadium was detected in only a single blubber sample. Mercury appears to be the most toxicologically significant metal with concentrations in the liver well above the current action level for mercury in fish. The concentrations of aluminum, arsenic, silver, cadmium and lead were present in one-fourth to two-thirds of all samples and were at either comparable or below concentrations previously reported. Neither gender nor region had a significant effect on metal burdens. Future work should consider metal concentrations in juveniles and adults and toxicological studies need to be performed to begin to assess the toxicity of these metals.  相似文献   

Cs baseline levels in the Mediterranean and Black Sea: A cross-basin survey of the CIESM Mediterranean Mussel Watch programme     

Herv Thbault  Alessia M. Rodriguez y Baena  Bruno Andral  Delko Barisic  Jos Benedicto Albaladejo  Alexandru S. Bologa  Redouane Boudjenoun  Roberta Delfanti  Victor N. Egorov  Tahar El Khoukhi  Heleni Florou  Goran Kniewald  Abdelkader Noureddine  Vasile Patrascu  Mai Khanh Pham  Alfonso Scarpato  Nikolay A. Stokozov  Sayhan Topcuoglu  Michel Warnau 《Marine pollution bulletin》2008,57(6-12):801

The common mussel Mytilus galloprovincialis was selected as unique biomonitor species to implement a regional monitoring programme, the CIESM Mediterranean Mussel Watch (MMW), in the Mediterranean and Black Seas. As of today, and upon standardization of the methodological approach, the MMW Network has been able to quantify ¹³⁷Cs levels in mussels from 60 coastal stations and to produce the first distribution map of this artificial radionuclide at the scale of the entire Mediterranean and Black Seas. While measured ¹³⁷Cs levels were found to be very low (usually <1 Bq kg⁻¹ wet wt) ¹³⁷Cs activity concentrations in the Black Sea and North Aegean Sea were up to two orders of magnitude higher than those in the western Mediterranean Basin. Such effects, far from representing a threat to human populations or the environment, reflect a persistent signature of the Chernobyl fallout in this area.  相似文献   

Reply by Dr. Robert J. Lawrence     

Robert J. Lawrence 《Marine pollution bulletin》2008,56(7):1381

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"A cautionary tale...after oil spills". Reply by Dr. Robert J. Lawrence     

Lawrence RJ 《Marine pollution bulletin》2008,56(7):1381

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Estimation of sediment sources using selected chemical tracers in the Perry lake basin,Kansas,USA   总被引：1，自引：0，他引：1  

K. E. JURACEK  A. C. ZIEGLER 《国际泥沙研究》2009,24(1):108-125

The ability to achieve meaningful decreases in sediment loads to reservoirs requires a determination of the relative importance of sediment sources within the contributing basins. In an investigation of sources of fine-grained sediment （clay and silt） within the Perry Lake Basin in northeast Kansas, representative samples of channel-bank sources, surface-soil sources （cropland and grassland）, and reservoir bottom sediment were collected, chemically analyzed, and compared. The samples were sieved to isolate the 〈63μt m fraction and analyzed for selected nutrients （total nitrogen and total phosphorus）, organic and total carbon, 25 trace elements, and the radionuclide cesium-137 （^137Cs）. On the basis of substantial and consistent compositional differences among the source types, total nitrogen （TN）, total phosphorus （TP）, total organic carbon （TOC）, and ^137Cs were selected for use in the estimation of sediment sources. To further account for differences in particle-size composition between the sources and the reservoir bottom sediment, constituent ratio and clay-normalization techniques were used. Computed ratios included TOC to TN, TOC to TP, and TN to TP. Constituent concentrations （TN, TP, TOC） and activities （^137Cs） were normalized by dividing by the percentage of clay. Thus, the sediment-source estimations involved the use of seven sediment-source indicators. Within the Perry Lake Basin, the consensus of the seven indicators was that both channel-bank and surface-soil sources were important in the Atchison County Lake and Banner Creek Reservoir subbasins, whereas channel-bank sources were dominant in the Mission Lake subbasin. On the sole basis of ^137Cs activity, surface-soil sources contributed the most free-grained sediment to Atchison County Lake, and channel-bank sources contributed the most fine-grained sediment to Banner Creek Reservoir and Mission Lake. Both the seven-indicator consensus and ^137Cs indicated that channelbank sources were dominant for Perry Lake and that channel-bank sources increased in importance with distance downstream in the basin.  相似文献   

Partitioned multiobjective risk modeling of carcinogenic compounds in groundwater     

Lawrence D. Lemke  Andrew S. Bahrou 《Stochastic Environmental Research and Risk Assessment (SERRA)》2009,23(1):27-39

Quantifying human cancer risk arising from exposure to contaminated groundwater is complicated by the many hydrogeological, environmental, and toxicological uncertainties involved. In this study, we used Monte Carlo simulation to estimate cancer risk associated with tetrachloroethene (PCE) dissolved in groundwater by linking three separate models for: (1) reactive contaminant transport; (2) human exposure pathways; and (3) the PCE cancer potency factor. The hydrogeologic model incorporates an analytical solution for a one-dimensional advective–dispersive–reactive transport equation to determine the PCE concentration in a water supply well located at a fixed distance from a continuous source. The pathway model incorporates PCE exposure through ingestion, inhalation, and dermal contact. The toxicological model combines epidemiological data from eight rodent bioassays of PCE exposure in the form of a composite cumulative distribution frequency curve for the human PCE cancer potency factor. We assessed the relative importance of individual model variables through their correlation with expected cancer risk calculated in an ensemble of Monte Carlo simulations with 20,000 trials. For the scenarios evaluated, three factors were most highly correlated with cancer risk: (1) the microbiological decay constant for PCE in groundwater, (2) the linear groundwater pore velocity, and (3) the cancer potency factor. We then extended our analysis beyond conventional expected value risk assessment using the partitioned multiobjective risk method (PMRM) to generate expected-value functions conditional to a 1 in 100,000 increased cancer risk threshold. This approach accounts for low probability/high impact outcomes separately from the conventional unconditional expected values. Thus, information on potential worst-case outcomes can be quantified for decision makers. Using PMRM, we evaluated the cost-benefit relationship of implementing several postulated risk management alternatives intended to mitigate the expected and conditional cancer risk. Our results emphasize the importance of hydrogeologic models in risk assessment, but also illustrate the importance of integrating environmental and toxicological uncertainty. When coupled with the PMRM, models integrating uncertainty in transport, exposure, and potency constitute an effective risk assessment tool for use within a risk-based corrective action (RBCA) framework.  相似文献