The onset of anthropogenic activity recorded in lake sediments in the vicinity of the Horne smelter in Quebec,Canada: Sulfur isotope evidence     

B. Mayer  S. Alpay  W.D. Gould  L. Lortie  F. Rosa 《Applied Geochemistry》2007

Contents and δ³⁴S values of several S compounds, enumerations of S-reducing bacteria (SRB) and Fe-reducing bacteria (IRB), and Fe, Pb and In concentrations were determined for ²¹⁰Pb-dated sediment cores from two lakes in Quebec, Canada. Both lakes are located approximately 70 km downwind of the Horne smelter and refinery in Rouyn-Noranda. Increases in Fe, Pb and In concentrations and a decrease in the δ³⁴S values of total S in both lake sediment cores coincide with the start-up of the smelter in 1927. The shift towards more negative δ³⁴S values was primarily caused by an increase in the extent of S isotope fractionation during bacterial (dissimilatory) SO₄ reduction due to SO₄ loading of the lakes after smelting began. Consequently, an enhanced accumulation of ³²S-enriched reduced inorganic S compounds is evident in the sediments. δ³⁴S values of organic S in the sediments decreased only slightly due to the smelter emissions between 1930 and 1980. Hence, due to the sulfide depositing mechanisms, S isotope ratios constitute a useful tracer recording the onset of S pollution in sediments of the two previously SO₄-limited lakes investigated. In contrast, total S concentrations alone are not reliable indicators for anthropogenic S loading in lake sediment records.  相似文献   

On the Relationship Between Queer and Feminist Geographies     

Larry Knopp 《The Professional geographer》2007,59(1):47-55

Despite their diverse and contested characters, queer and feminist geographies have much in common historically, theoretically, empirically, and politically. Following a brief discussion of their connections and divergences, I discuss the distinctive contributions of queer geographies and their potential, in continuing conversation and alliance with feminist geographies, to enliven and enrich geographical inquiry more broadly. I focus particularly on the potential of feminist‐inspired and allied queer geographies to rethink a variety of spatial (and other) ontologies, including space, place, placelessness, movement, gender, homophobias and heterosexisms, generational cultures, and cultural politics.  相似文献   

Estimation of fault-zone conductance by calibration of a regional groundwater flow model: Desert Hot Springs,California   总被引：1，自引：2，他引：1  

Alex Mayer  Wesley May  Chad Lukkarila  Jimmy Diehl 《Hydrogeology Journal》2007,15(6):1093-1106

The hydraulic conductance of a large fault zone has been estimated by calibrating a regional groundwater flow model. Drops in groundwater elevations of over 80 m have been observed along a 15-km length of the Mission Creek fault, California, USA. The large drops in elevation are attributed to the reduced hydraulic conductivity of the fault materials. A conceptual and numerical model of the two hydrologic subbasins in Desert Hot Springs, separated by the Mission Creek fault, was developed. The model was used to estimate the hydraulic conductance along the fault. The parameter estimation involved calibrating the model with observed groundwater elevations from over 40 locations over a 60-year period. The fault hydraulic conductances were estimated assuming a linear trend in the fault length, yielding variations in the fault hydraulic conductance of about an order of magnitude along the fault length (2?×?10^?11–4?×?10^?10 1/s). When an average fault thickness of 35 m is assumed, the fault hydraulic conductivity values are estimated to be from three to five orders of magnitude lower than the surrounding materials. A sensitivity analysis indicated that assumptions made in the conceptual model do not significantly affect estimated fault hydraulic conductances.  相似文献   

Analysis of Low-Frequency Turbulence Above Tall Vegetation Using a Doppler Sodar     

Christoph Thomas  Jens-Christopher Mayer  Franz X. Meixner  Thomas Foken 《Boundary-Layer Meteorology》2006,119(3):563-587

This study applies acoustic sounding to observe coherent structures in the roughness sublayer (RSL) above tall vegetated surfaces. Data were collected on 22 days during two separate field experiments in summer 2003. A quality control scheme was developed to ensure high data quality of the collected time series. The data analysis was done using both discrete and continuous wavelet transform. The flow in the RSL was found to be a superposition of dynamic Kelvin–Helmholtz instabilities and convective mixing. The characteristic time scales for coherent structures resulting from the dynamic instabilities were observed to be approximately 20–30 s while thermal eddies have much larger time scales of 190–210 s. The degree of vertical coherency in the RSL increases with the flow evolving from neutral to near-convective conditions. This increase in the degree of organisation is attributed to the evolution of attached thermal eddies. The coherent structures resulting from instabilities were found to be present throughout the RSL but do not contribute to the increased vertical coherency. An alternative conceptual approach for the definition of the RSL is proposed, which yields its maximum vertical extent to five times the canopy height.  相似文献   

A family of spectral target signature transforms: relationship to the past, new transforms, and sensitivity tests     

Mayer  R. Bucholtz  F. Scribner  D. Kruer  M. 《Geoscience and Remote Sensing Letters, IEEE》2004,1(1):26-30

Previous studies introduced, examined, and tested a variety of registration-free transformations, specifically the diagonal, whitening/dewhitening, and target CV (covariance) transformations, that temporally evolve spectral signatures under varying conditions. Target spectral signatures were transformed using imagery of spatially overlapping regions from datasets collected at different times. This letter shows that these previously studied registration-free transformations can be described using a single general equation and form a subset of a family of valid transforms. Further, this letter finds only a small reduction in target detection results from using nonoverlapping but similar regions to transform target signatures in matched filter searches. The diagonal, whitening/dewhitening, and target CV transformations appear in this formulation as having integral exponent parameter n (n = 0, 1, 2, respectively). These transformed target signatures, used in matched filter searches, were tested on images taken from two very different data collects using different sensors, targets, and backgrounds. In one dataset, the transform was applied to multispectral images taken from an airborne longwave infrared sensor binned to 30 bands. The other dataset used images of a variety of targets that were collected using broad-band, bore-sighted, staring array sensors sensitive to visible, shortwave infrared, midwave infrared, and longwave infrared wavelengths. Transformation performance was tested using target-to-clutter ratio (TCR) and receiver operator characteristic (ROC) curve. Transforms with exponents between 0 and 2 yielded the largest TCR and remained relatively constant. Optimal exponents for the transformation were target dependent for both datasets. Further, only minimal reduction in TCR was observed for transforms (O < n < 2) that had no shared overlapping regions, although the areas used to transform the spectral signatures shared similar content (trees, roads, etc.).  相似文献   

U–Pb perovskite ages for brazilian kamafugitic rocks: further support for a temporal link to a mantle plume hotspot track     

Patrícia B. A. Sgarbi  Larry M. Heaman  Jos Carlos Gaspar 《Journal of South American Earth Sciences》2004,16(8):95

We present the results of a U–Pb perovskite age study of kamafugites from Mata da Corda (MC) and Santo Antônio da Barra (SAB), Minas-Goiás alkaline province, Brazil. Perovskite crystals were separated from MC mafurites, ugandites, and cognate pyroxenites, as well as from SAB melilite mafurite. The range of ages of Brazilian kamafugitic samples is 15 Ma. The ²⁰⁶Pb/²³⁸U perovskite ages generally cluster into three age groupings: 88–90, 80–81, and 75–76 Ma. The two younger periods of kamafugitic magmatism occur in the MC area, whereas the older samples are from the SAB area. These new age results provide the first robust evidence of a progressive eastward younging of mafic alkaline magmatism, most likely related to a mantle plume hotspot track.  相似文献   

Automated isotopic measurements of micron-sized dust: application to meteoritic presolar silicon carbide     

Larry R. Nittler  Conel M.O'D. Alexander 《Geochimica et cosmochimica acta》2003,67(24):4961-4980

We report the development of a new analytical system allowing the fully automated measurement of isotopic ratios in micrometer-sized particles by secondary ion mass spectrometry (SIMS) in a Cameca ims-6f ion microprobe. Scanning ion images and image processing algorithms are used to locate individual particles dispersed on sample substrates. The primary ion beam is electrostatically deflected to and focused onto each particle in turn, followed by a peak-jumping isotopic measurement. Automatic measurements of terrestrial standards indicate similar analytical uncertainties to traditional manual particle analyses (e.g., ∼3‰/amu for Si isotopic ratios). We also present an initial application of the measurement system to obtain Si and C isotopic ratios for ∼3300 presolar SiC grains from the Murchison CM2 carbonaceous chondrite. Three rare presolar Si₃N₄ grains were also identified and analyzed. Most of the analyzed grains were extracted from the host meteorite using a new chemical dissolution procedure. The isotopic data are broadly consistent with previous observations of presolar SiC in the same size range (∼0.5-4 μm). Members of the previously identified SiC AB, X, Y, and Z subgroups were identified, as was a highly unusual grain with an extreme ³⁰Si enrichment, a modest ²⁹Si enrichment, and isotopically light C. The stellar source responsible for this grain is likely to have been a supernova. Minor differences in isotopic distributions between the present work and prior data can be partially explained by terrestrial contamination and grain aggregation on sample mounts, though some of the differences are probably intrinsic to the samples. We use the large new SiC database to explore the relationships between three previously identified isotopic subgroups—mainstream, Y, and Z grains—all believed to originate in asymptotic giant branch stars. The isotopic data for Z grains suggest that their parent stars experienced strong CNO-cycle nucleosynthesis during the early asymptotic giant branch phase, consistent with either cool bottom processing in low-mass (M < 2.3M_⊙) parent stars or hot-bottom burning in intermediate-mass stars (M > 4M_⊙). The data provide evidence for a sharp threshold in metallicity, above which SiC grains form with much higher ¹²C/¹³C ratios than below. Above this threshold, the fraction of grains with relatively high ¹²C/¹³C decreases exponentially with increasing ²⁹Si/²⁸Si ratio. This result indicates a sharp increase in the maximum mass of SiC parent stars with decreasing metallicity, in contrast to expectations from Galactic chemical evolution theory.  相似文献   

Comparative Rates of Western Juniper Afforestation in South‐Central Oregon and the Role of Anthropogenic Disturbance*     

Peter T. Soul  Paul A. Knapp  Henri D. Grissino‐Mayer 《The Professional geographer》2003,55(1):43-55

We examine changes in canopy cover for adult western juniper from the 1960s to 1994 in central Oregon using repeat aerial photography. We compare changes at four sites with a land‐use history of minimal anthropogenic disturbance to changes on adjacent sites that have a disturbance history more typical of central Oregon rangelands. Canopy cover increased at all sites, but afforestation on sites with domestic livestock grazing was greater. The potential driving forces common to all sites include a long fire‐free interval, early twentieth‐century favorable climatic conditions, biological inertia, and atmospheric CO₂ enrichment.  相似文献   

Radial Velocities of Six Early Type Evolved Stars     

Pavel Mayer  Magdy A. Hanna  Marek Wolf  Drahos Chochol 《Astrophysics and Space Science》1998,262(2):163-169

Many early-type main sequence stars are known spectroscopic binaries, while early type spectroscopic binaries with evolved components are rather rare and well-determined masses are available only in some cases. For this reason a program to study stars with suspected variable velocity among early-type evolved stars has been initiated some time ago. In the present paper 54 coudé spectra for a sub-group formed of six early-type stars, namely HD 7902, HD 28446, HD 42087, HD 187983, HD 195592 and HD 208501 have been measured and the results of these plates have been presented.  相似文献   

Decadal and millennial velocities of rock glaciers, Selwyn Mountains, Canada   总被引：1，自引：0，他引：1  

Valerie F. Sloan  Larry D. Dyke 《Geografiska Annaler: Series A, Physical Geography》1998,80(3-4):237-249

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