Two serendipitous low-mass LMC clusters discovered with HST1     

Basílio X. Santiago  Rebecca A. W. Elson  Steinn Sigurdsson  & Gerard F. Gilmore 《Monthly notices of the Royal Astronomical Society》1998,295(4):860-868

We present V and I photometry of two open clusters in the LMC down to V ∼26. The clusters were imaged with the Wide Field and Planetary Camera 2 (WFPC2) on board the Hubble Space Telescope ( HST ), as part of the Medium Deep Survey Key Project. Both are low-luminosity ( M_V ∼−3.5), low-mass ( M ∼10³ M⊙) systems. The chance discovery of these two clusters in two parallel WFPC2 fields suggests a significant incompleteness in the LMC cluster census near the bar. One of the clusters is roughly elliptical and compact, with a steep light profile, a central surface brightness μ _V (0)∼20.2 mag arcsec⁻², a half-light radius r _hl∼0.9 pc (total visual major diameter D ∼3 pc) and an estimated mass M ∼1500 M⊙. From the colour–magnitude diagram and isochrone fits we estimate its age as τ∼(2–5)×10⁸ yr. Its mass function has a fitted slope of Γ=Δlogφ( M )/Δlog M =−1.8±0.7 in the range probed (0.9≲ M /M⊙≲4.5). The other cluster is more irregular and sparse, having shallower density and surface brightness profiles. We obtain Γ=−1.2±0.4, and estimate its mass as M ∼400 M⊙. A derived upper limit for its age is τ≲5×10⁸ yr. Both clusters have mass functions with slopes similar to that of R136, a massive LMC cluster, for which HST results indicate Γ∼−1.2. They also seem to be relaxed in their cores and well contained in their tidal radii.  相似文献   

Dissolved and particulate organic carbon in Chesapeake Bay     

Thomas R. Fisher  James D. Hagy  Emma Rochelle-Newall 《Estuaries and Coasts》1998,21(2):215-229

We measured dissolved and particulate organic carbon (DOC and POC) in samples collected along 13 transects of the salinity gradient of Chesapeake Bay. Riverine DOC and POC end-members averaged 232±19 μM and 151±53 μM, respectively, and coastal DOC and POC end-members averaged 172±19 μM and 43±6 μM, respectively. Within the chlorophyll maximum, POC accumulated to concentrations 50–150 μM above those expected from conservative mixing and it was significantly correlated with chlorophylla, indicating phytoplankton origin. POC accumulated primarily in bottom waters in spring, and primarily in surface waters in summer. Net DOC accumulation (60–120 μM) was observed within and downstream of the chlorophyll maximum, primarily during spring and summer in both surface and bottom waters, and it also appeared to be derived from phytoplankton. In the turbidity maximum, there were also net decreases in chlorophylla (?3 μg l^?1 to ?22 μg l^?1) and POC concentrations (?2 μM to ?89 μM) and transient DOC increases (9–88 μM), primarily in summer. These occurred as freshwater plankton blooms mixed with turbid, low salinity seawater, and we attribute the observed POC and DOC changes to lysis and sedimentation of freshwater plankton. DOC accumulation in both regions of Chesapeake Bay was estimated to be greater than atmospheric or terrestrial organic carbon inputs and was equivalent to ≈10% of estuarine primary production.  相似文献   

Vibracoring from lake ice with a lightweight monopod and piston coring apparatus     

Timothy G. Fisher 《Journal of Paleolimnology》2004,31(3):377-382

A monopod and piston coring apparatus for coring water-saturated sediment is described. The lightweight apparatus can be used from either an ice platform or the ground surface and can be transported by aircraft. Using a piston, core recovery is increased to better than 90%, and depending upon the monopod height, 7 m-long cores can be obtained. Tips for coring in freezing temperatures are also given.  相似文献   

Igneous zircon: trace element composition as an indicator of source rock type   总被引：225，自引：2，他引：225  

E. Belousova  W. Griffin  Suzanne Y. O'Reilly  N. Fisher 《Contributions to Mineralogy and Petrology》2002,143(5):602-622

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A freshwater population of the mummichog,Fundulus heteroclitus,from the Susquehanna River drainage in Pennsylvania     

Robert F. Denoncourt  Jack C. Fisher  Kevin M. Rapp 《Estuaries and Coasts》1978,1(4):269-272

An established population of mummichog,Fundulus heteroclitus, in the Susquehanna drainage is reported from Pennsylvania for the first time. Three year classes of this brackish water species were taken on 17 August 1976 from Letort Spring Run, a tributary of the Conodoguinet Creek in Cumberland County. A survey of unpublished records and museum specimens revealed occurrences in Wissahickon Creek, Montgomery County, and Brandywine Creek, Chester County; both Delaware drainage. Presence in these drainages is believed the result of bait bucket introduction.  相似文献   

Correction of ground-water chemistry and carbon isotopic composition for effects of CO₂ outgassing     

F.J. Pearson  Donald W. Fisher  L.N. Plummer 《Geochimica et cosmochimica acta》1978,42(12):1799-1807

Direct measurements on water samples from several CO₂-charged warm springs are significantly higher than values calculated from field pH and alkalinity (and other constituents). In addition, calcite saturation indices calculated from field pH and solution composition indicated supersaturation in samples which, on the basis of hydrogeologic concepts, should be near saturation or undersaturated. We attribute these discrepancies to uncertainties in field pH, resulting from CO₂ outgassing during pH measurement. Because samples for direct measurement can be taken with minimal disturbance to the water chemistry, we have used the measured to back calculate an estimate of the field pH and the carbon isotopic composition of the water before outgassing. By reconstructing water chemistry in this way, we find generally consistent grouping of $\text{δ}{}^{13}\text{C}$, pH, and degree of calcite saturation in samples taken from the same source at different times, an observation which we expect based on our understanding of the hydrogeology and geochemistry of the ground-water systems. This suggests that for very careful geochemical work, particularly on ground-waters much above ambient temperature, measurements may provide more information on the system and a better estimate of its state of saturation with respect to carbonate minerals than can field measurements of pH.  相似文献   

Geoanalytic applications of particle tracks     

David E. Fisher 《Earth》1975,11(4):291-335

Since the discovery that ionizing tracks left by highly energetic nuclei can be made visible through optical microscopes by proper etching, the field of particle track studies has blossomed at a rate equalled only by the growth of the porno-film industry. The analytic applications alone are probably unique in the wide range of results and fields of study that have evolved from a single technique.PTA has been used to study the abundance and distribution of the lightest elements, Li and B, and the heaviest elements, U and Th, in every conceivable type of matrix, from blood to ultramafic rocks, in every conceivable locale, from the bottom of the seas to the surface of the moon. It has been used to study the distribution in the cosmic radiation of all the naturally-occurring chemical elements, to search in our laboratories and in extra-terrestrial samples for superheavy elements that no one has yet succeeded in making, and to search in all samples accessible to us for those exotic creations of the intellect, magnetic monopoles.And, since the rate of publication of PTA papers is still — in 1974 — accelerating, the second dozen years should be even more bewildering than the first.  相似文献   

Mixed messages in iron oxide–copper–gold systems of the Cloncurry district,Australia: insights from PIXE analysis of halogens and copper in fluid inclusions     

Timothy Baker  Roger Mustard  Bin Fu  Patrick J. Williams  Guoyi Dong  Louise Fisher  Geordie Mark  Chris G. Ryan 《Mineralium Deposita》2008,43(6):599-608

Proterozoic rocks of the Cloncurry district in NW Queensland, Australia, are host to giant (tens to hundreds of square kilometers) hydrothermal systems that include (1) barren regional sodic–calcic alteration, (2) granite-hosted hydrothermal complexes with magmatic–hydrothermal transition features, and (3) iron oxide–copper–gold (IOCG) deposits. Fluid inclusion microthermometry and proton-induced X-ray emission (PIXE) show that IOCG deposits and the granite-hosted hydrothermal complexes contain abundant high temperature, ultrasaline, complex multisolid (type 1) inclusions that are less common in the regional sodic–calcic alteration. The latter is characterized by lower salinity three-phase halite-bearing (type 2) and two-phase (type 3) aqueous inclusions. Copper contents of the type 1 inclusions (>300 ppm) is higher than in type 2 and 3 inclusions (<300 ppm), and the highest copper concentrations (>1,000 ppm) are found both in the granite-hosted systems and in inclusions with Br/Cl ratios that are consistent with a magmatic source. The Br/Cl ratios of the inclusions with lower Cu contents are consistent with an evaporite-related origin. Wide ranges in salinity and homogenization temperatures for fluid inclusions in IOCG deposits and evidence for multiple fluid sources, as suggested by halogen ratios, indicate fluid mixing as an important process in IOCG genesis. The data support both leaching of Cu by voluminous nonmagmatic fluids from crustal rocks, as well as the direct exsolution of Cu-rich fluids from magmas. However, larger IOCG deposits may form from magmatic-derived fluids based on their higher Cu content.  相似文献   

Isotopic composition of sulfate as a tracer of natural and anthropogenic influences on groundwater geochemistry in an urban sandstone aquifer, Birmingham, UK   总被引：1，自引：0，他引：1  

Simon Bottrell  John Tellam  Rebecca Bartlett  Anwen Hughes   《Applied Geochemistry》2008,23(8):2382-2394

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Semantics, Metadata, Geographical Information and Users   总被引：1，自引：1，他引：0  

Alexi J Comber  Peter F Fisher  Richard A Wadsworth 《Transactions in GIS》2008,12(3):287-291

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