4.8 – 20 μm Imaging of orion BN/KL: II. A new look at luminosity sources and the role of IRc2     

Daniel Y. Gezari  Dana E. Backman 《Experimental Astronomy》1994,3(1-4):45-52

We have reconsidered the energetics of the BN/KL infrared complex, using array images at nine wavelengths between 4.8 and 20 m, and find a much lower luminosity for IRc2 than the generally accepted value. The new observations resolve larcsec structure throughout the region, including several new compact sources within a few arcsec of IRc2 and significant details imaged in the 9.7 m silicate feature. Together with other recent work, the results suggest that luminous stars associated with three compact HII regions found within BN/KL, rather than IRc2, may be the more significant luminosity sources for the complex.  相似文献   

Pharmaceuticals and Other Organic Waste Water Contaminants Within a Leachate Plume Downgradient of a Municipal Landfill   总被引：1，自引：0，他引：1  

Kimberlee K. Barnes  Scott C. Christenson  Dana W. Kolpin  Michael J. Focazio  Edward T. Furlong  Steven D. Zaugg  Michael T. Meyer  Larry B. Barber 《Ground Water Monitoring & Remediation》2004,24(2):119-126

Ground water samples collected from the Norman Landfill research site in central Oklahoma were analyzed as part of the U.S. Geological Survey (USGS) Toxic Substances Hydrology Program's national reconnaissance of pharmaceuticals and other organic waste water contaminants (OWCs) in ground water. Five sites, four of which are located downgradient of the landfill, were sampled in 2000 and analyzed for 76 OWCs using four research methods developed by the USGS. OWCs were detected in water samples from all of the sites sampled, with 22 of the 76 OWCs being detected at least once. Cholesterol (a plant and animal steroid), was detected at all five sites and was the only compound detected in a well upgradient of the landfill. N,N-diethyltoluamide (DEBT used in insect repellent) and tri(2-chloroethyl) phosphate (fire-retardant) were detected in water samples from all four sites located within the landfill-derived leachate plume. The sites closest to the landfill had more detections and greater concentrations of each of the detected compounds than sites located farther away. Detection of multiple OWCs occurred in the four sites located within the leachate plume, with a minimum of four and a maximum of 17 OWCs detected. Because the landfill was established in the 1920s and closed in 1985, many compounds detected in the leachate plume were likely disposed of decades ago. These results indicate the potential for long-term persistence and transport of some OWCs in ground water.  相似文献   

Successful Use of an Innovative Horizontal/Vertical Well Couplet in Fractured Bedrock to Intercept a Mobile Gasoline Plume     

Dana Carlisle  David A. Cook  James A. Miller 《Ground Water Monitoring & Remediation》2002,22(2):82-87

The horizontal directional drilling (HDD) technology was successfully used in a fracture-controlled sandstone matrix to intercept a gasoline plume and create a 150-foot-long hydrodynamic barrier preventing seepage of gasoline and contaminated ground water into a salmon-bearing stream within a public park. A 36-foot-deep vertical recovery well (VW) intercepts the central low point of the 420-foot-long HDD borehole to pump recovered fluids. Contaminant seepage into the creek ceased within hours of starting up the HDD/VW interceptor system in August 1999. Approximately 325 gallons of gasoline and 2 million gallons of contaminated ground water have been recovered to date.  相似文献   

CO₂-forced climate thresholds during the Phanerozoic     

Dana L. Royer 《Geochimica et cosmochimica acta》2006,70(23):5665-5675

The correspondence between atmospheric CO₂ concentrations and globally averaged surface temperatures in the recent past suggests that this coupling may be of great antiquity. Here, I compare 490 published proxy records of CO₂ spanning the Ordovician to Neogene with records of global cool events to evaluate the strength of CO₂-temperature coupling over the Phanerozoic (last 542 my). For periods with sufficient CO₂ coverage, all cool events are associated with CO₂ levels below 1000 ppm. A CO₂ threshold of below ∼500 ppm is suggested for the initiation of widespread, continental glaciations, although this threshold was likely higher during the Paleozoic due to a lower solar luminosity at that time. Also, based on data from the Jurassic and Cretaceous, a CO₂ threshold of below ∼1000 ppm is proposed for the initiation of cool non-glacial conditions. A pervasive, tight correlation between CO₂ and temperature is found both at coarse (10 my timescales) and fine resolutions up to the temporal limits of the data set (million-year timescales), indicating that CO₂, operating in combination with many other factors such as solar luminosity and paleogeography, has imparted strong control over global temperatures for much of the Phanerozoic.  相似文献   

Pesticides in Ground Water of the United States, 1992–1996     

Dana W. Kolpin  Jack E. Barbash  Robert J. Gilliom 《Ground water》2000,38(6):858-863

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A record of Holocene environmental and ecological changes from Wildwood Lake,Long Island,New York     

W. Wyatt Oswald  David R. Foster  Elaine D. Doughty  Dana Macdonald 《第四纪科学杂志》2010,25(6):967-974

Analyses of pollen, charcoal and organic content in a lake sediment core from Wildwood Lake, Long Island, New York, provide insights into the ecological and environmental history of this region. The early Holocene interval of the record (ca. 9800–8800 cal. a BP) indicates the presence of Pinus rigida–Quercus ilicifolia woodlands with high fire activity. A layer of sandy sediment dating to 9200 cal. a BP may reflect a brief period of reduced water depth, consistent with widespread evidence for cold, dry conditions at that time. Two other sandy layers, bracketed by ¹⁴C dates, represent a sedimentary hiatus from ca. 8800 to 4500 cal. a BP. This discontinuity may reflect the removal of some sediment during brief periods of reduced water depth at 5300 and 4600 cal. a BP. In the upper portion of the record (<4500 cal. a BP), subtle changes at ca. 3000 cal. a BP indicate declining prevalence of Quercus–Fagus–Carya forests and increasing abundance of Pinus rigida, perhaps due to reduced summer precipitation. Elevated percentages of herbaceous taxa in the uppermost sediments represent European agricultural activities. However, unlike charcoal records from southern New England, fire activity does not increase dramatically with European settlement. These findings indicate that present‐day Pinus rigida–Quercus ilicifolia woodlands on eastern Long Island are not a legacy of recent, anthropogenic disturbances. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Estimating Aerodynamic Parameters of Urban-Like Surfaces with Heterogeneous Building Heights   总被引：4，自引：4，他引：0  

J. T. Millward-Hopkins  A. S. Tomlin  L. Ma  D. Ingham  M. Pourkashanian 《Boundary-Layer Meteorology》2011,141(3):443-465

There are many geometrical factors than can influence the aerodynamic parameters of urban surfaces and hence the vertical wind profiles found above. The knowledge of these parameters has applications in numerous fields, such as dispersion modelling, wind loading calculations, and estimating the wind energy resource at urban locations. Using quasi-empirical modelling, we estimate the dependence of the aerodynamic roughness length and zero-plane displacement for idealized urban surfaces, on the two most significant geometrical characteristics; surface area density and building height variability. A validation of the spatially-averaged, logarithmic wind profiles predicted by the model is carried out, via comparisons with available wind-tunnel and numerical data for arrays of square based blocks of uniform and heterogeneous heights. The model predicts two important properties of the aerodynamic parameters of surfaces of heterogeneous heights that have been suggested by experiments. Firstly, the zero-plane displacement of a heterogeneous array can exceed the surface mean building height significantly. Secondly, the characteristic peak in roughness length with respect to surface area density becomes much softer for heterogeneous arrays compared to uniform arrays, since a variation in building height can prevent a skimming flow regime from occurring. Overall the simple model performs well against available experimental data and may offer more accurate estimates of surface aerodynamic parameters for complex urban surfaces compared to models that do not include height variability.  相似文献   

Uncertainties in determining microbial biomass C using the chloroform fumigation–extraction method     

Daniel S. Alessi  Dana M. Walsh  Jeremy B. Fein 《Chemical Geology》2011,280(1-2):58-64

We tested the accuracy of the chloroform fumigation–extraction method, which is commonly used to determine soil biomass C concentrations. Accurate and precise determination of total microbial biomass is important in order to characterize soil properties and to develop predictive metal transport models for soils. Two natural soils, and individual soil components, including silica sand, montmorillonite, kaolinite, a humic acid, and Bacillus subtilis bacterial cells, were fumigated for 24 h. Following the fumigation, C from fumigated and unfumigated samples was extracted using a 0.5 M K₂SO₄ solution. The difference between the C content in the fumigated and unfumigated samples ideally represents C due to biomass because the fumigation procedure should lyse cells and release biomass C. We observed increased C release upon fumigation for bacteria-only samples, confirming the ability of fumigation to lyse cells. There was no difference in extracted C concentration between fumigated and unfumigated samples of silica sand and of humic acid, confirming that the fumigation process does not introduce additional organic C to samples of these soil components. However, the fumigated clay samples both showed increased C release relative to the unfumigated controls, indicating that significant concentrations of the fumigant, chloroform, adsorbed onto the clay minerals studied here. Additionally, we found significant chloroform remaining in the extracts from two fumigated natural soils. Attempts to remove the chloroform from the soils or soil components prior to extraction by increasing the evacuation time, or to remove chloroform in the extracts by sparging them vigorously with nitrogen gas, both failed. This research reveals that chloroform gas may adsorb significantly to clays and the clay fraction of natural soils. Thus, the fumigation–extraction method must be corrected to account for the added chloroform C and accurately assess the concentration of biomass C in soils that contain significant concentrations of clays.  相似文献   

Scale‐Dependent Variability of As and Heavy Metals in a River Elbe Floodplain     

Dana Zimmer  Kristian Kiersch  Christel Baum  Ralph Meissner  Robert Müller  Gerald Jandl  Peter Leinweber 《洁净——土壤、空气、水》2011,39(4):328-337

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Repeated century-scale droughts over the past 13,000 yr near the Hudson River watershed, USA     

Paige E. Newby  Bryan N. Shuman  Jeffrey P. Donnelly  Dana MacDonald 《Quaternary Research》2011,75(3):523-530

Long-term sediment and ground-penetrating radar data from Davis Pond, a small lake near the Hudson River valley, reveal past droughts in a historically humid region that presently supplies water to millions of people in and around New York City. A minimum of eleven sandy paleoshoreline deposits in the lake date from 13.4 to 0.6 cal ka BP. The deposits span 1500 to 200 yr between bracketing radiocarbon ages, and intrude into lacustrine silts up to 9.0 m below the modern lake surface in a transect of six sediment cores. Three low stands, ca. 13.4–10.9, 9.2 and 8.2 cal ka BP indicate low regional moisture balance when low temperatures affected the North Atlantic region. Consistent with insolation trends, water levels rose from ca. 8.0 cal ka BP to present, but five low stands interrupted the rise and are likely associated with ocean–atmosphere interactions. Similar to evidence from other studies, the data from Davis Pond indicate repeated multi-century periods of prolonged or frequent droughts super-imposed on long-term regional trends toward high water levels. The patterns indicate that water supplies in this heavily populated region have continuously varied at multiple time scales and confirm that humid regions such as the northeastern United States are more prone to severe drought than historically expected.  相似文献