A Rationale for the National Center for Geographic Information and Analysis     

Jerome E. Dobson 《The Professional geographer》1993,45(2):207-215

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Isotopic variations of the nitrogen in Lake Superior     

Patrick C Pang  Jerome O Nriagu 《Geochimica et cosmochimica acta》1977,41(6):811-814

The isotopic compositions of nitrogen in lake water, plankton samples and the organic-N fractions extracted from sediments at selected stations in Lake Superior are presented. The δ¹⁵N values of the Kjeldahl total-N and acid hydrolyzable-N in the lake sediments are similar (range, +4.7–+6.7; mean, +5.5 %.). The δ¹⁵N data for the various extracts are independent of the age and concentration of nitrogen in the sediments. On the other hand, the δ¹⁵N values of lake water (+ 0.6‰), phytoplankton (+ 1.6 %.) and Zooplankton (+ 5.0‰) in the water column suggest significant discrimination against the heavier nitrogen isotope in the food chain of the lacustrine environment. The data emphasize the need for a better understanding of the autogenous isotopic fractionation before the isotopic method can be used to fingerprint the sources of nitrogen in a limnetic ecosystem.  相似文献   

Coronal hole evolution by sudden large scale changes     

Jerome T. Nolte  Michel Gerassimenko  Allen S. Krieger  Craig V. Solodyna 《Solar physics》1978,56(1):153-159

We have compared sudden shifts in coronal hole boundaries observed by the S-054 X-ray telescope on Skylab between May and November, 1973, within 1 day of CMP of the holes, at latitudes 40 °, with the long-term evolution of coronal hole area. We find that large-scale shifts in boundary locations can account for most if not all of the evolution of coronal holes. The temporal and spatial scales of these large-scale changes imply that they are the results of a physical process occurring in the corona. We conclude that coronal holes evolve by magnetic field lines opening when the holes are growing, and by fields closing as the holes shrink.Skylab Solar Workshop post-doctoral appointee 1975–1976. The Skylab Solar Workshops are sponsored by NASA and NSF and managed by the High Altitude Observatory, National Center for Atmospheric Research.  相似文献   

Metamorphic sole formation,emplacement and blueschist facies overprint: early subduction dynamics witnessed by western Turkey ophiolites   总被引：2，自引：0，他引：2       下载免费PDF全文

Alexis Plunder  Philippe Agard  Christian Chopin  Mathieu Soret  Aral I. Okay  Hubert Whitechurch 《地学学报》2016,28(5):329-339

The largest ophiolite on Earth, in western Turkey, is a key place to study obduction and early subduction dynamics. Ophiolite remnants derived from the same Neotethyan branch (preserved as a result of long‐lived Late Cretaceous continental subduction and later obduction) are underlain by hundred‐metre‐thick extensive metamorphic soles. These soles formed synchronously, at c. 93 Ma, and were welded to the base of the ophiolite, thereby dating the start of intra‐oceanic subduction. This contribution focuses on the structure, petrology and pressure–temperature evolution of the soles and other subduction‐derived units. Peak pressure–temperature conditions were estimated at 10.5 ± 2 kbar and 800 ± 50 °C for the sole by means of pseudosection calculations using Theriak/Domino and at 12 kbar and 425 °C for the unique, enigmatic blueschist facies overprint of the sole. This study provides clues to the mechanisms of sole underplating during early subduction, later cooling, and the nature of the western Turkey ophiolite.  相似文献   

A regional Bayesian POT model for flood frequency analysis     

Mathieu Ribatet  Eric Sauquet  Jean-Michel Grésillon  Taha B. M. J. Ouarda 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(4):327-339

Flood frequency analysis is usually based on the fitting of an extreme value distribution to the local streamflow series. However, when the local data series is short, frequency analysis results become unreliable. Regional frequency analysis is a convenient way to reduce the estimation uncertainty. In this work, we propose a regional Bayesian model for short record length sites. This model is less restrictive than the index flood model while preserving the formalism of “homogeneous regions”. The performance of the proposed model is assessed on a set of gauging stations in France. The accuracy of quantile estimates as a function of the degree of homogeneity of the pooling group is also analysed. The results indicate that the regional Bayesian model outperforms the index flood model and local estimators. Furthermore, it seems that working with relatively large and homogeneous regions may lead to more accurate results than working with smaller and highly homogeneous regions.  相似文献   

Ionospheric reflection coefficients at vlf from sferics measurements     

A. Glenn Jean Jr.  L. Jerome Lange  James R. Wait 《Pure and Applied Geophysics》1957,38(1):147-153

Summary A method for calculating the complex ionospheric reflection coefficients at vlf using sferic waveforms is presented. The mathematical analysis was carried out for a number of different waveforms to illustrate the method. Reflection coefficients determined from sferics observations were compared with those calculated using an ionospheric model. In most cases, the agreement with theory is fairly good although in some cases, reflection coefficients exceeding unity were obtained. The discrepancies are believed to result from horizontally polarized flashes rather than limitations in the ionospheric model.  相似文献   

Biotic forcing militates against river meandering in the modern Bonneville Basin of Utah     

Alessandro Ielpi  Mathieu G. A. Laptre 《Sedimentology》2019,66(5):1896-1929

Biotic forcing on river meandering is a highly debated topic in sedimentology. Vegetation is assumed to hold a vital role on channel stability and sinuosity, for example through bank stabilization and pedogenic production of cohesive clays. However, statistically solid and causal relationships between vegetation density and river sinuosity remain largely untested in natural systems. This study investigates physical and biotic forcings on channel sinuosity in the Bonneville Basin of Utah (USA), an endorheic depression flanked by active fluvial networks (‘washes’) that display diverse vegetation density and channel‐planform style. By means of remote sensing and ground‐data collection, 58 washes are considered, 0·1 to 90 km² in surface area and drained by trunk channels <45 m wide and <1·2 m deep. Each wash is composed of a catchment basin connected downstream to an aggradational and distributive channel network. Statistically solid regressions highlight the primary roles played by base level and catchment size on fluvial morphogenesis. In contrast, no correlation is found between vegetation density and other parameters such as trunk‐channel width or surface area of the largest meander in a wash. Similarly, no statistical correlation exists between vegetation density and meander size or sinuosity index. Rather, larger and more sinuous meanders are invariably associated with lower vegetation density. These results are corroborated by field evidence showing that sparse vegetation promotes flow disturbance, channel branching and bar braiding instead of stabilizing sediment surfaces. Thus, river meandering is attributed to cohesion offered by mud retention within the endorheic basin, as well as discharge and stream‐power modulation along bifurcating and low‐gradient channel reaches. Hence, this work demonstrates how meandering‐channel patterns may arise from entirely physical forcings in the absence of vegetation.  相似文献   

Causes and consequences of bimodal grain-size distribution of tephra fall deposited during the August 2006 Tungurahua eruption (Ecuador)   总被引：2，自引：2，他引：0  

Julia Eychenne  Jean-Luc Le Pennec  Liliana Troncoso  Mathieu Gouhier  Jean-Marie Nedelec 《Bulletin of Volcanology》2012,74(1):187-205

The violent August 16–17, 2006 Tungurahua eruption in Ecuador witnessed the emplacement of numerous scoria flows and the deposition of a widespread tephra layer west of the volcano. We assess the size of the eruption by determining a bulk tephra volume in the range 42–57 × 10⁶ m³, which supports a Volcanic Explosivity Index 3 event, consistent with calculated column height of 16–18 km above the vent and making it the strongest eruptive phase since the volcano’s magmatic reactivation in 1999. Isopachs west of the volcano are sub-bilobate in shape, while sieve and laser diffraction grain-size analyses of tephra samples reveal strongly bimodal distributions. Based on a new grain-size deconvolution algorithm and extended sampling area, we propose here a mechanism to account for the bimodal grain-size distribution. The deconvolution procedure allows us to identify two particle subpopulations in the deposit with distinct characteristics that indicate dissimilar transport-depositional processes. The log-normal coarse-grained subpopulation is typical of particles transported downwind by the main volcanic plume. The positively skewed, fine-grained subpopulation in the tephra fall layer shares close similarities with the elutriated co-pyroclastic flow ash cloud layers preserved on top of the scoria flow deposits. The area with the higher fine particle content in the tephra layer coincides with the downwind prolongation of the pyroclastic flow deposits. These results indicate that the bimodal distribution of grain size in the Tungurahua fall deposit results from synchronous deposition of lapilli from the main plume and fine ash elutriated from scoria flows emplaced on the western flank of the volcano. Our study also reveals that inappropriate grain-size data processing may produce misleading determination of eruptive type.  相似文献   

Soil temperature and CO2 degassing,SO2 fluxes and field observations before and after the February 29, 2016 new vent inside Nyiragongo crater     

Charles M. Balagizi  Mathieu M. Yalire  Honoré M. Ciraba  Vicky B. Kajeje  Abel S. Minani  Annie B. Kinja  Marcellin M. Kasereka 《Bulletin of Volcanology》2016,78(9):64

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Sex‐specific affinity for redox‐active metals influences antioxidant responses of Callinectes amnicola (blue crab) populations in littoral and open water habitats of a tropical coastal lagoon          下载免费PDF全文

Fisayo Christie Jerome  Adesola A Hassan  Azubuike Victor Chukwuka 《Marine Ecology》2017,38(3)

The critical role of ecological preferences and opportunity in determining contaminant uptake and adaptive responses of sexes in the wild is still poorly understood. This ecological relationship was investigated by measuring metal bioaccumulation and antioxidant activity in male and female blue crab populations from open water habitat and the littoral/inter‐tidal zone of the Lagos Lagoon. A total of 741 samples of blue crab (littoral zone: 263 females, 137 males; open water zone, 230 females, 111 males) was collected monthly over 24 months (January 2010–January 2012) from each site and the measurements of morphometric features (wet weight, carapace length, carapace width) were recorded; condition index, metal (redox active: Cu, Zn, redox inactive: Pb, Cd) concentration in tissues (gills, hepatopancreas, gonads and muscle) and antioxidant activity (superoxide dismutase, reduced glutathione, glutathione peroxidase, catalase and malondialdehyde) were measured for each sex. Monthly sediment samples for both habitats were also analysed for metals using standard methods. Female crabs were significantly larger (p < .05) with a better condition index than the male crabs across sites and seasons, while higher oxidative damage was recorded in male crabs in the littoral zone compared to the open water zone. The results show that there was a negative association between antioxidant activity and lipid peroxidation; a negative relationship between concentrations of redox‐inactive metals (Pb and Cd) and antioxidant activity in male crab tissues; and a positive relationship between uptake of a redox‐active metal (Cu) and antioxidant activity in female crab tissues. Although these trends suggest sex‐specific toxicity, they also associate redox‐inactive metals with the downregulation of antioxidant activity and oxidative stress. Furthermore, the higher condition index of females corroborates the possibility of sex‐specific toxicity, while the larger‐sized females compared to males suggests size‐sexual dimorphism in the blue crab populations. The site‐specific oxidative damage between sexes may be attributed to the different complexity of both habitats, which affords different ecological opportunities for the sexes.  相似文献