Cusps in cold dark matter haloes     

Jürg Diemand  Marcel Zemp  Ben Moore  Joachim Stadel  Marcella Carollo 《Monthly notices of the Royal Astronomical Society》2005,364(2):665-673

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Hilde Stenuit  Róbert Erdélyi  Marcel Goossens 《Solar physics》1995,161(1):139-157

The present paper discusses the implementation of the SGHR method (Sakurai, Goossens, and Hollweg, 1991; Goossens, Ruderman, and Hollweg, 1995) in a numerical scheme for determining resonantly driven Alfvén waves in nonuniform magnetic flux tubes. This method is based on jump conditions over the dissipative layer which are obtained from an asymptotic analysis of analytical solutions to simplified versions of the linear non-ideal MHD equations in this dissipative layer. The emphasis is on the computational simplicity and the accuracy of the method. The method derives its computational simplicity from the fact that it circumvents the numerical integration of the non-ideal MHD equations. The implementation only requires the numerical integration of the ideal MHD equations away from the resonant position. There is no need for a special integration scheme and a PC suffices as a hardware tool.The accuracy of the method is verified by means of test computations. These test computations deal with the loss of power of acoustic waves in sunspots by resonant absorption of Alfvén waves. Results for the absorption coefficients obtained with the SGHR method are compared with known results in the literature obtained by integration of the full set of the linearized non-ideal MHD equations. The agreement is excellent and identifies the SGHR method as a powerful and extremely easy to use tool for studying resonant Alfvén waves.  相似文献   

Reply to the comments on “The biosphere: A homogenizer of Pb-isotope signals” by Richard Bindler and William Shotyk     

Clemens Reimann  Belinda Flem  Arnold Arnoldussen  Peter Englmaier  Tor Erik Finne  Friedrich Koller   ystein Nordgulen 《Applied Geochemistry》2008,23(8):2527-2535

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The biosphere: A homogeniser of Pb-isotope signals     

Clemens Reimann  Belinda Flem  Arnold Arnoldussen  Peter Englmaier  Tor Erik Finne  Friedrich Koller  Øystein Nordgulen 《Applied Geochemistry》2008

Rock, soil, and plant (terrestrial moss, European mountain ash leaves, mountain birch leaves, bark and wood, and spruce needles and wood) samples, collected at 3 km intervals along a 120 km long transect (40 sites) cutting the city of Oslo, Norway, were analysed for their Pb concentration and Pb-isotope ratios. A general decrease in ²⁰⁶Pb/²⁰⁷Pb, ²⁰⁸Pb/²⁰⁷Pb and ²⁰⁶Pb/²⁰⁸Pb ratios, with a characteristic low variability in all plant materials and the plant-derived O-horizon of soil profiles, compared to rocks and mineral soils, is observed along the transect. It is demonstrated that minerogenic and biogenic sample materials belong to two different spheres, the lithosphere and biosphere, and that geochemical processes determining their chemical and isotopic compositions differ widely. Background variation for both sample materials needs to be established and documented at the continental and global scale before the anthropogenic influence on the geochemistry of the earth’s surface can be reliably estimated.  相似文献   

Completeness of citizen science biodiversity data from a volunteered geographic information perspective     

Clemens Jacobs  Alexander Zipf 《地球空间信息科学学报》2017,20(1):3-13

Observations of living organisms by citizen scientists that are reported to online portals are a valuable source of information. They are also a special kind of volunteered geographic information (VGI). VGI data have issues of completeness, which arise from biases caused by the opportunistic nature of the data collection process. We examined the completeness of bird species represented in citizen science observation data from eBird and iNaturalist in US National Parks (NPs). We used approaches for completeness estimation which were developed for data from OpenStreetMap, a crowdsourced map of the world. First, we used an extrinsic approach, comparing species lists from citizen science data with National Park Service lists. Second, we examined two intrinsic approaches using total observation numbers in NPs and the development of the number of new species being added to the data-set over time. Results from the extrinsic approach provided appropriate completeness estimations to evaluate the intrinsic approaches. We found that total observation numbers are a good estimator of species completeness of citizen science data from US NPs. There is also a close relationship between species completeness and the ratio of new species added to observation data vs. observation numbers in a given year.  相似文献   

Melt production during granulite-facies anatexis: experimental data from “primitive” metasedimentary protoliths   总被引：11，自引：0，他引：11  

Gary Stevens  John D. Clemens  Giles T. R. Droop 《Contributions to Mineralogy and Petrology》1997,128(4):352-370

We conducted fluid-absent partial melting experiments, at 0.5 and 1.0?GPa in the temperature range 750 to 1000?°C, to investigate the influence of bulk rock Mg ? [100Mg/(Mg+Fe)] and the effects of additional TiO₂ on the granulite-grade anatectic evolution of relatively magnesian metapelites and metagreywackes. In these experiments, melting began between 780 and 830?°C by the incongruent breakdown of biotite to produce quartz-saturated, granulite-facies residual mineral assemblages in equilibrium with H₂O-undersaturated granitic melt. The glass (quenched melt) compositions produced in this study vary little. Generally, the glasses have compositions similar to those of many natural strongly peraluminous leucogranites. The solidus temperatures in both rock types increase with increasing Mg ?, but are unaffected by the presence or absence of a TiO₂ component. At 0.5?GPa the metapelites melted at temperatures up to 50?°C lower than the equivalent metagreywackes, but at 1?GPa there was no discernible difference. This study suggests that the fluid-absent solidus has a steep positive dP/dT slope in metapelites and steep negative dP/dT slope in metagreywackes. The pattern of melt production with increasing temperature is strongly controlled by the upper limit of biotite stability. In TiO₂-free compositions this was found to increase by 15 to 20?°C in the metapelites and by 30 to 40?°C in the metagreywackes, as a function of increasing Mg ? from 49 to 81. The presence of a TiO₂ component increases the upper limit of biotite stability by ～50?°C in the metapelites and by ～80?°C in the metagreywackes, over that observed in the equivalent TiO₂-free compositions. In consequence, in the TiO₂-free samples large pulses of melt (up to 35 wt%) are produced over narrow temperature ranges (as little as 15?°C in these experiments) between 830 and 875?°C. In the TiO₂-bearing samples the major pulse of melt production occurs more gradually between 830 and >900?°C.  相似文献   

Strain and flow in the metamorphic core complex of Ios Island (Cyclades,Greece)     

Marcel Mizera  Jan H. Behrmann 《International Journal of Earth Sciences》2016,105(7):2097-2110

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Urban Community Garden Agrodiversity and Cultural Identity in Philadelphia,Pennsylvania, U.S.          下载免费PDF全文

Hamil Pearsall  Sheila Gachuz  Marcel Rodriguez Sosa  Birgit Schmook  Hans van der Wal  Maria Amalia Gracia 《Geographical review》2017,107(3):476-495

Considerable research has examined the social, cultural, economic, and community benefits of urban gardening. Few studies, however, have empirically assessed factors that influence urban community garden agrodiversity or its relationship to these dimensions of gardening. We conducted an interdisciplinary study of agrodiversity and cultural identity, based certain markers of identity, including how people see themselves with respect to race, ethnicity, or place of origin, in community gardens in Philadelphia, Pennsylvania. We conducted fifty‐six semistructured interviews with gardeners with different cultural identities in eight community gardens on their motivations for urban community gardening during 2014. We conducted plant inventories of the corresponding garden plots and found 104 cultivated edible and ornamental species and 28 varieties representing 34 families. We find that although gardens with culturally diverse gardeners did not have higher species richness, the cultural identity of the gardeners influenced species selection and reason for gardening. Further, the structure, design and species composition of garden plots reflected the identities of garden members. These finding have implications for the recent institutionalization of urban agriculture into city land policies in Philadelphia and other cities in North America.  相似文献   

Tektonische Forschungen in den Appalachen     

Clemens Lebling 《International Journal of Earth Sciences》1914,5(7):449-462

Ohne Zusammenfassung  相似文献   

Fisheries compliance in South Africa: A decade of challenges and reform 1994–2004     

Maria Hauck  Marcel Kroese 《Marine Policy》2006

In South Africa, fishery managers have struggled with a number of challenges in terms of compliance amidst a process of legal and policy reform since the democratic elections of 1994. The past 10 years, and more specifically the past five, have seen a significant change in compliance effort, with a particular focus on increasing law enforcement activities and capacity. This paper highlights two case studies that have been instrumental in restructuring fisheries compliance in South Africa. Although law enforcement has been significantly strengthened, greater political will and government commitment is required to implement alternative strategies that will have a long-term impact on levels of compliance.  相似文献