An ultrasoft X-ray source (RX 215319−1514) and discovery of a narrow‐line Seyfert 1 galaxy     

Kulinder Pal Singh  Laurence R. Jones 《Monthly notices of the Royal Astronomical Society》2000,312(2):380-386

We present results on the identification of the optical counterpart of an ultrasoft X-ray source discovered with ROSAT . Two optical candidates – a galaxy and a star – are found within the error circle of the X-ray source position. Optical spectroscopy of the two candidates reveals that (a) the galaxy is a narrow-line Seyfert type 1 galaxy, and (b) the star is a late A-type or an early F-type. The F _x F _v ratio is too high for the star to be the counterpart of the X-ray source, but consistent with that for an active galaxy. Although higher-resolution X-ray imaging of the region is needed to definitely settle the question of the counterpart of the X-ray source, the narrow-line Seyfert 1 galaxy is the best candidate. The spectral properties of the newly discovered narrow-line Seyfert 1 galaxy are also presented, including its extreme X-ray power-law spectral index of Γ≥4.  相似文献   

Di-nitrogen fixation in a eutrophic tropical bay     

Laurence D. Mee  Roberto Cortes-Altamirano  Luz-Maria Garcia-de-la-Parra 《Estuarine, Coastal and Shelf Science》1984,19(4):477-483

Di-nitrogen fixation, measured in situ by the acetylene reduction technique, was shown to be associated with regular summer blooms of Oscillatoria erythraea in Mazatlán bay, a eutrophic tropical embayment on the Pacific Coast of Mexico. The Oscillatoria population density and the rate of di-nitrogen fixation per cell were of similar magnitude to those observed by other workers in the oligotrophic Caribbean Sea. Since the non-nitrogen limited fraction (Oscillatoria) of the total population was generally less than 10% and the nutrient supply to the bay is relatively abundant, di-nitrogen fixation does not appear to play an important role in the eutrophication of the bay.  相似文献   

High‐resolution evolution of terrigenous sediment yields in the Provence Basin during the last 6 Ma: relation with climate and tectonics          下载免费PDF全文

Estelle Leroux  Marina Rabineau  Daniel Aslanian  Christian Gorini  Stéphane Molliex  Francois Bache  Cécile Robin  Laurence Droz  Maryline Moulin  Jeffrey Poort  Jean‐Loup Rubino  Jean‐Pierre Suc 《Basin Research》2017,29(3):305-339

Basin‐wide correlation of Messinian units and Plio‐Quaternary chronostratigraphic markers (5.3 Ma, 2.6 Ma, 0.9 Ma and 0.45 Ma), the mapping of total sediment thickness and the determination of overall sedimentary volumes enabled us to provide a high‐resolution quantitative history of sediment volumes for the last 6 Ma along the Gulf of Lions margin. The results point to (i) a dramatic increase in terrigenous sediment input during the Messinian Salinity Crisis. This increased sedimentation reflects enhanced regional fluvial erosion related to the dramatic fall of Mediterranean base‐level. Stronger weathering due to a regional wetter climate probably also increased erosional fluxes. (ii) A sediment input three times higher during the Plio‐Quaternary compared to the Miocene seems in agreement with published measurements from World's ocean. However, the timing of this increase being uncertain, it implies that the trigger(s) also remain(s) uncertain. (iii) A decrease in detrital volume around 2.6 Ma is attributed to a regional change in the drainage pattern of rivers in the northwestern Alps. (iv) This study also highlights the Mid‐Pleistocene Revolution around 0.9 Ma, which resulted in an almost doubling of sediment input in the Provencal Basin.  相似文献   

Seasonal influence of the sea surface temperature on the low atmospheric circulation and precipitation in the eastern equatorial Atlantic     

Rémi Meynadier  Gaëlle de Coëtlogon  Marion Leduc-Leballeur  Laurence Eymard  Serge Janicot 《Climate Dynamics》2016,47(3-4):1127-1142

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CryoSheds: a GIS modeling framework for delineating land-ice watersheds for the Greenland Ice Sheet     

Lincoln H Pitcher  Laurence C. Smith  Colin J. Gleason  Kang Yang 《地理信息系统科学与遥感》2016,53(6):707-722

Choice of watershed delineation technique is an important source of uncertainty for cryo-hydrologic studies of the Greenland Ice Sheet (GrIS), with different methods yielding different watersheds for a common pour point. First, this paper explores this uncertainty for the Akuliarusiarsuup Kuua River Northern Tributary, Western Greenland. Next, a standardized, semi-automated modeling framework for generating land-ice watersheds for GrIS land-terminating ice (henceforth referred to as CryoSheds) using geographic information systems (GIS) hydrologic modeling tools is presented. The framework uses ArcGIS and the ArcPy geoprocessing library to delineate two types of land-ice watersheds, namely those defined by: (1) a hydraulic pressure potential with varying water to ice overburden pressure ratios (k-value), which determines theoretical flow paths from the hydrostatic equation, using surface and bedrock digital elevation models (DEMs) and (2) a surface topography DEM alone. Lastly, a demonstration of the CryoSheds method is presented for seven remotely sensed proglacial pour points along the Aussivigssuit River (AR), Western Greenland, and its largest tributaries. GrIS meltwater runoff from these seven nested land-ice watersheds is estimated using Modele Atmospherique Regional (MAR) v.3.2 and runoff uncertainties due to watershed delineation parameter selection is estimated.  相似文献   

Nonlinear aspects of sea surface temperature in Monterey Bay     

Laurence C. Breaker 《Progress in Oceanography》2006,69(1):61-89

Nonlinear aspects of sea surface temperature (SST) in Monterey Bay are examined, based on an 85-year record of daily observations from Pacific Grove, California. Oceanic processes that affect the waters of Monterey Bay are described, processes that could contribute to nonlinearity in the record. Exploratory data analysis reveals that the record at Pacific Grove is non-Gaussian and, most likely, nonstationary. A more recent test for stationarity based on a power law approximation to the slope of the power spectrum indicates that the record is stationary for frequencies up to ∼8 cycles per year (∼45 days), but nonstationary at higher frequencies. To examine the record at Pacific Grove for nonlinear behavior, third-order statistics, including the skewness, statistical measures of asymmetry, the bicorrelation, and the bispectrum, were employed. The bicorrelation revealed maxima located approximately 365 days apart, reflecting a nonlinear contribution to the annual cycle. Based on a 365-day moving window, the running skewness is positive almost 80% of the time, reflecting the overall impact of warming influences. The asymmetry is positive approximately 75% of the time, consistent with the asymmetric shape of the mean annual cycle. Based on the skewness and asymmetry, nonlinearities in the record, when they occur, appear to be event-driven with time scales possibly as short as several days, to several years. In many cases, these events are related to warm water intrusions into the bay, and El Niño warming episodes.The power spectrum indicates that the annual cycle is a dominant source of variability in the record and that there is a relatively strong semiannual component as well. To determine whether or not the annual and semiannual cycles are harmonically related, the bispectrum and bicoherence were calculated. The bispectrum is nonzero, providing a strong indication of nonlinearity in the record. The bicoherence indicates that the annual cycle is a major source of nonlinearity and further implies that the annual and semiannual cycles are harmonically related. Based on the wavelet power spectrum (WPS), the appearance of the semiannual cycle is transitory; however, pathways between the annual and semiannual cycles appear at certain times when nonlinear interaction between them could occur. Comparisons between the WPS and the running skewness suggest that there is a tendency for periods when pathways exist, to coincide with increased positive skewness, and, often, with El Niño warming episodes. The Hilbert-Huang transform, a relatively new tool for nonstationary and nonlinear spectral analysis, was used to further examine the origin of the semiannual cycle. The time-dependent Hilbert spectrum reveals large and erratic variations in frequency associated with semiannual cycle but far greater stability associated with the annual cycle. As a result, the time-integrated Hilbert spectrum does not indicate the presence of a semiannual cycle. The method of surrogates from the field of nonlinear dynamics was also employed to test the Hopkins record for nonlinearity. Differences between the data and the surrogates were found that were statistically significant, implying the existence of nonlinearity in the record. Using the method of surrogates together with a one-year moving window, El Niño warming episodes appear to be a likely source of nonlinearity, consistent with the other analyses that were performed. Finally, the influence of stochastic variability due to serial correlation in the data was examined by comparing standardized statistics for the observations and for simulations based on an autoregressive model whose properties were obtained from the observations. The magnitude of the variability for the simulations was found to be far less than that associated with the original data, and thus stochastic variability does not appear to be a factor that significantly affects the interpretation of our results.  相似文献   

Molecular investigations into pollutant impact on roundnose grenadier (C. rupestris) and transplanted common mussel (M. edulis) in Skagerrak, the North Sea     

Lars Frlin  David R. Livingstone  Kerstin Magnusson  Laurence D. Peters  Montserrat Sol  Anders Sjlin  ke Granmo 《Marine environmental research》1996,42(1-4)

The use of a suite of different biochemical markers in the deep sea fish Roundnose grenadier and caged common mussels, and analyses of contaminant levels in the mussels, indicate that Skagerrak are more polluted than waters around the Faroe Islands. In Roundnose, induction of ethoxyresorufin-O-deethylase (EROD) is consistent with increased benzo(a)pyrene hydroxylase (BPH) in mussels and elevated levels of polynuclear aromatic hydrocarbons (PAHs) in mussels and sediment from Skagerrak. This evidence of a large-scale environmental impact of pollutants should lead to further efforts to decrease transport into, and deposition of, waste compounds in the Skagerrak area.  相似文献   

Mixed and Multi-Stock Fisheries     

Kell  Laurence T.; Crozier  Walter W.; Legault  Christopher M. 《ICES Journal of Marine Science》2004,61(8):1330

The September 2003 ICES Annual Science Conference was held inTalinn, Estonia, and Theme Session V was "Mixed and multi-stockfisheries – challenges and tools for assessments, prediction,and management." The theme session brought together researchersfrom the salmonid and marine fishery fields to address commonproblems faced when multiple fleets harvest a common stock,  相似文献   

Effect of intertidal compared to subtidal exposure on the uptake,loss and oxidative toxicity of water-born benzo[a]pyrene in the mantle and whole tissues of the mussel,Mytilus edulis L     

Durand F  Peters LD  Livingstone DR 《Marine environmental research》2002,54(3-5):271-274

Blue mussels (Mytilus edulis, L.) were exposed to a single dose of 1 ppb benzo[a]pyrene (BaP) under subtidal (SC) or tidal conditions (TC; 6 h immersion, 6 h emersion) in order to follow its bioaccumulation in whole mussel and mantle tissue, and to compare BaP-mediated toxicity on lipids (malonaldehyde formation, MDA) in the mantle. Rapid uptake of BaP (70-80% of BaP initially introduced in tanks) was observed in both conditions after 12 h, but subsequent depuration in clean water was slower in TC mussels. BaP levels decreased in whole tissue in both conditions between 12 and 24 h, but increased in mantle. The mantle BaP levels were similar during the first 4 days in SC and TC, but whereas they decreased in SC after 7 days. BaP was retained at high levels in mantle in TC until the end of the study (14 days). In both conditions, significant increases (P < 0.05) in lipid peroxidation were observed after 4 days, but MDA levels were approximately 3 times higher in the mantle of TC than SC mussels, although BaP tissue concentrations were similar. These observations suggested that increased BaP-mediated toxicity in mantle lipid was due to the interactive effect of the tidal cycle of immersion/emersion on BaP-mediated oxidative damage.  相似文献   

Implications of climate change for the management of North Sea cod (Gadus morhua)   总被引：1，自引：0，他引：1  

Kell  Laurence T.; Pilling  Graham M.; O'Brien  Carl M. 《ICES Journal of Marine Science》2005,62(7):1483-1491

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