Evolution and Fragmentation of Wide-Angle Wind Driven Molecular Outflows     

Andrew Cunningham  Adam Frank  Peggy Varnière  Alexei Poludnenko  Sorin Mitran  Lee Hartmann 《Astrophysics and Space Science》2005,298(1-2):317-322

We present two dimensional cylindrically symmetric hydrodynamic simulations and synthetic emission maps of a stellar wind propagating into an infalling, rotating environment. The resulting outflow morphology, collimation and stability observed in these simulations have relevance to the study of young stellar objects, Herbig-Haro jets and molecular outflows. Our code follows hydrogen gas with molecular, atomic and ionic components tracking the associated time dependent molecular chemistry and ionization dynamics with radiative cooling appropriate for a dense molecular gas. We present tests of the code as well as new simulations which indicate the presence of instabilities in the wind-blown bubble’s swept-up shell.  相似文献   

Galaxy evolution: Inhomogeneous halo collapse     

Jeannette M. Myers  Dieter H. Hartmann  Lih-Sin The 《Astrophysics and Space Science》2003,284(2):787-790

In an effort to study the halo globular clusters we perform a simulation of inhomogeneous halo collapse using a SPH/N-body code. We include dark matter particles, (cooling) gas, and stars. Supernova feedback is included as a heat source for the gas in the local environment of star forming regions. We find this model cannot reproduce the age distribution and spatial distribution of halo globular clusters. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Paleoindication of acidification in Kleiner Arbersee (Federal Republic of Germany,Bavarian Forest) by chydorids,chrysophytes, and diatoms     

Chrisitian Steinberg  Helga Hartmann  Klaus Arzet  Dieter Krause-Dellin 《Journal of Paleolimnology》1988,1(2):149-157

In a sediment core of Lake Kleiner Arbersee, located in the Bavarian Forest on gneiss bedrock and with spodosolic soils in the catchment, acidification was reconstructed using assemblages of chydorids, scaled chrysophytes, and diatoms as paleoindicators. All paleoindicators demonstrated acidification of Kleiner Arbersee. There were marked differences, however, in the extent of the indicated acidification: In lower layers, where scaled chrysophytes and chydorids clearly indicate beginning acidification, pH-decline inferred by diatoms lies within the standard deviation, and is statistically not significant until the 7 cm layer. We conclude that mallomonadaceans reflect the acidification of the water body and strongly respond to the lowest seasonal pH, as their indicated rate of acidification is higher than that of diatoms, which appear to more closely indicate the pH of the sediment/water interface, especially when the pH of the water column has dropped below ca. 5.5. Chydorids may additionally be influenced by proton release of dense Sphagnum-stands, which cover the littoral of Kleiner Arbersee completely.We dedicate this paper to Prof. Dipl.-Ing. L. Strobel, who encouraged new perspectives in limnological water management, on the occasion of his 65^th anniversary.  相似文献   

Atmospheric CO₂ consumption by chemical weathering in North America     

Nils Moosdorf  Jens Hartmann  Benjamin Hagedorn 《Geochimica et cosmochimica acta》2011,75(24):7829-7854

CO₂ consumption by chemical weathering is an integral part of the boundless carbon cycle, whose spatial patterns and controlling factors on continental scale are still not fully understood. A dataset of 338 river catchments throughout North America was used to empirically identify predictors of bicarbonate fluxes by chemical weathering and interpret the underlying controlling factors. Detailed analysis of major ion ratios enables distinction of the contributions of silicate and carbonate weathering and thus quantifying CO₂ consumption. Extrapolation of the identified empirical model equations to North America allows the analysis of the spatial patterns of the CO₂ consumption by chemical weathering.Runoff, lithology and land cover were identified as the major predictors of the riverine bicarbonate fluxes and the associated CO₂ consumption. Other influence factors, e.g. temperature, could not be established in the models. Of the distinguished land cover classes, artificial surfaces, dominated by urban areas, increase bicarbonate fluxes most, followed by shrubs, grasslands, managed lands, and forests. The extrapolation results in an average specific bicarbonate flux of 0.3 Mmol km⁻² a⁻¹ by chemical weathering in North America, of which 64% originates from atmospheric CO₂, and 36% from carbonate mineral dissolution. Chemical weathering in North America thus consumes 50 Mt atmospheric CO₂-C per year. About half of that originates from 10% of the area of North America.The estimated strength of individual predictors differs from previous studies. This highlights the need for a globally representative set of regionally calibrated models of CO₂ consumption by chemical weathering, which apply very detailed spatial data to resolve the heterogeneity of earth surface processes.  相似文献   

Compatibility of space and time for modeling fluvial HCO3- fluxes – A comparison     

Nils Moosdorf  Jens Hartmann  Ronny Lauerwald 《Applied Geochemistry》2011

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Modelling Estuarine Biogeochemical Dynamics: From the Local to the Global Scale     

Pierre Regnier  Sandra Arndt  Nicolas Goossens  Chiara Volta  Goulven G. Laruelle  Ronny Lauerwald  Jens Hartmann 《Aquatic Geochemistry》2013,19(5-6):591-626

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Fault imaging in sparsely sampled 3D seismic data using common‐reflection‐surface processing and attribute analysis – a study in the Upper Rhine Graben     

Hermann A. Buness  Hartwig von Hartmann  Hanna‐Maria Rumpel  Charlotte M. Krawczyk  Rüdiger Schulz 《Geophysical Prospecting》2014,62(3):443-452

Cost reduction in seismic reconnaissance is an issue in geothermal exploration and can principally be achieved by sparse acquisition. To address the adherent decrease in signal/noise ratio, the common‐reflection‐surface method has been proposed. We reduced the data density of an existing 3D dataset and evaluated the results of common‐reflection‐surface processing using seismic attributes. The application of the common‐reflection‐surface method leads in all cases to an improvement of the signal/noise ratio. The most distinct improvement can be seen in the low fold regions. The improvement depends strongly on the midpoint aperture, and there is a tradeoff between reflector continuity and horizontal resolution. If small scale targets are to be imaged, a small aperture size is necessary, which may be far below the Fresnel zone for a specific reflector. The substantial reduction of the data density leads in our case to an irrecoverable information loss.  相似文献   

Fischwachstum bei Oligo-, Meso- und Eutrophie des Bodensees     

Dr. Jürgen Von Hartmann 《Aquatic Sciences - Research Across Boundaries》1978,40(1):32-39

Recent growth of 14 fish taxa of Lake Constance has been studied. In the mesotrophic basin summer-pelagic species opposite to the others appear to grow faster now than during earlier oligotrophic status. From trends of growth, feeding and yield (table) it is concluded that eutrophication has favoured planktivores.—In the eutrophic lower basin only coregonids grow slower than in the mesotrophic part of the lake. Factors that have caused growth differences are thought to be food density and water temperature (through changed fish distribution and different shape of basin).  相似文献   

Fischereiliche Veränderungen in kulturbedingt eutrophierenden Seen     

Dr. Jürgen Hartmann 《Aquatic Sciences - Research Across Boundaries》1977,39(2):243-254

Mainly from the trends of fish yield four stages of fish succession in European lakes under cultural eutrophication are described. Trends of transparency, phosphorus, weed, benthos, and plankton are included. Supplementary interrelated effects of eutrophication on fish biology (growth, fat content, condition, distribution, reproduction, parasites, fish kills, introgression, feeding) have been collected from literature. The effects, mainly observed on planktivores, are not specific for species or localities.  相似文献   

Sm–Nd isotopic compositions as a proxy for magmatic processes during the Neoproterozoic of the southern Brazilian shield     

Maria do Carmo P. Gastal  Jean Michel Lafon  Lo Afraneo Hartmann  Edinei Koester 《Journal of South American Earth Sciences》2005,18(3-4):255-276

Combined analyses of Nd isotopes from a wide range of Neoarchaean–Cretaceous igneous rocks provides a proxy to study magmatic processes and the evolution of the lithosphere. The main igneous associations include the Neoproterozoic granitoids from the southern Brazilian shield, which were formed during two tectonothermal events of the Brasiliano cycle: the São Gabriel accretionary orogeny (900–700 Ma) and the Dom Feliciano collisional orogeny (660–550 Ma). Rocks related to the formation of the São Gabriel arc (900–700 Ma) mainly have a depleted juvenile signature. For the Neoproterozoic collisional event, the petrogenetic discussion focuses on two old crustal segments and three types of mantle components. However, no depleted juvenile material was involved in the formation of the Dom Feliciano collisional belt (800–550 Ma), which implies an ensialic environment for the Dom Feliciano orogeny. In the western Neoproterozoic foreland, records of a Neoarchaean lower crust predominate, whereas a Paleoproterozoic crust does in the eastern Dom Feliciano belt. The western foreland includes two amalgamated geotectonic domains, the São Gabriel arc and Taquarembó block. In the collisional belt, the old crust was intensely reworked during the São Gabriel event. In addition to the Neoproterozoic subduction-processed subcontinental lithosphere (São Gariel arc), we recognize two old enriched mantle components, which also are identified in the Paleoproterozoic intraplate tholeiites from Uruguay and the Cretaceous potassic suites from eastern Paraguay. One end member displays the prominent influence of Trans-Amazonian (2.3–2.0 Ga) or older subduction events, whereas the other can be interpreted as a reenrichment of the first during the latest Trans-Amazonian collisional or younger events. This reenriched mantle is documented in late Neoproterozoic suites from the western foreland (605–550 Ma) and younger suites from the eastern collisional belt (600–580 Ma). The other enriched mantle component with an old subduction signature, however, appears only in older rocks of the collisional belt (800–600 Ma). The participation of the subduction-related Brasiliano mantle as an end member of binary mixing occurred in some early Neoproterozoic suites (605–580 Ma) from the western foreland, but the contribution of the Neoarchaean lower crust increased near the late igneous event (575–550 Ma).  相似文献