Indications of a biological and biochemical evolutionary trend during the archean and early proterozoic     

Bartholomew Nagy  Lois Anne Nagy  John E. Zumberge  Deborah S. Sklarew  Phillip Anderson 《Precambrian Research》1977,5(2):109-120

Micropaleontological observations and organic geochemical analyses imply, but certainly do not prove, that life may not have been present ～3,800 Ma ago in Southwestern Greenland; however, physiologically complex prokaryotes flourished by the Early Proterozoic in other locations. It is, of course, also possible that life may have appeared earlier in locations other than Greenland. Investigations of Precambrian biological and biochemical evolutionary trends require interdisciplinary efforts, up-to-date instrumentation and methodology (such as ultramicrochemical analyses of individual microfossils/microstructures), and caution in the interpretation of experimental results.  相似文献   

Seasonal changes in the composition of the diets of Peary caribou and muskoxen on Banks Island     

Nicholas C. Larter  John A. Nagy 《Polar research》2004,23(2):131-140

Caribou and muskoxen are the only ungulate species occupying Arctic tundra environments. We analysed plant fragments found in fresh (< 4 hr old) samples of faecal material to determine the diets of Peary caribou ( Rangifer tarandus pearyi ) and muskoxen ( Ovibos moschatus ) on Banks Island, Canada. Willow was a major component of the diets of both animals, dominating the caribou diet during summer and representing substantial proportions of the muskoxen diet during at least seven months of the year. The diet of caribou was more diverse than that of muskoxen and was dominated by sedge, willow ( Salix arctica ), legume ( Astragalus spp., Oxytropis spp.) and Dryas integrifolia . The diet of muskoxen was dominated by sedge and willow. There was substantial overlap (up to 70%) in the diets of these herbivores with the similarity more pronounced in areas of high muskox density ( ca. 1.65 ani mals/km²). We discuss herbivore diets in relation to foraging behaviour and forage availability.  相似文献   

A chart for the computation of the gravitational attraction of a right rectangular prism     

Dezsö Nagy 《Pure and Applied Geophysics》1973,102(1):5-14

Summary The gravity effect of a right rectangular prism is calculated by a graphical procedure. The basis of the calculation is an algorithm for the linear combination of readings taken from a chart which has as ordinates and abscissas the body coordinates of the prism normalized with respect to the depth to the top and bottom surfaces.Gravity Division, Earth Physics Branch, Department of Energy, Mines and Resources, Ottawa, Canada. Contribution No. 425.  相似文献   

Theoretical study of the electrostatic potential of an idealized semi-infinite crystal of talc and vibrational frequencies of an adsorbed proton     

Ladislav Turi Nagy  Daniel Tunega 《Physics and Chemistry of Minerals》1994,21(4):213-221

The electrostatic potential above a surface of a semi-infinite crystal of talc Mg₃Si₄O₁₀(OH)₂ in the idealized structure (layer group symmetry C2/m) was computed using the electron distribution obtained by a semiempirical INDO/2 calculation of the electron structure of one idealized layer. The potential of the semi-infinite crystal was obtained as the sum of contributions from an infinite number of individual layers. The adsorption enthalpy and the vibrational frequencies of a proton hypothetically adsorbed in vacuo were also computed.  相似文献   

Evaluating the Performance of Using PPK-GPS Technique in Producing Topographic Contour Map     

Ahmed El Shouny  Nagy Yakoub  Magdy Hosny 《Marine Geodesy》2017,40(4):224-238

The Global Positioning System (GPS) is considered as one of the most powerful tools that are used in geodetic works. It is increasingly considered as an alternative tool for conventional surveying techniques. The goal of this research paper is to produce a methodology for generating topographic contour maps using the post-processed kinematic differential GPS technique (PPK-GPS). The performance of this technique is assessed by comparing it with the traditional spirit-leveling technique taking into consideration the accuracy, time, and cost. The study area is located along the Mediterranean coast in the Rosetta area of the middle Delta in Egypt with a total area of about 39 km². The field work includes 14 control points and about 50,000 PPK observations. In addition, 20 check cross sections that extend along the coastal line from Rosetta to El Burullus cities were observed using both spirit-leveling and GPS-PPK techniques. The results of the comparison indicate that the PPK-GPS technique can be used instead of spirit leveling in producing a topographic contour map with an accuracy of about 20 cm in orthometric height. We find that the PPK-GPS technique reduces the estimated time of leveling works in our study area by about 70%.  相似文献   

Foraminiferal morphogroups in dysoxic shelf deposits from the Jurassic of Spitsbergen     

Jenö Nagy  Matías Reolid  & Francisco J. Rodríguez-Tovar 《Polar research》2009,28(2):214-221

Analysis of benthic foraminiferal assemblages was performed in Bathonian to Kimmeridgian deposits through a section covering the lower half of the Agardhfjellet Formation in central Spitsbergen. The section consists mainly of organic-rich shales, which contain low-diversity agglutinated assemblages. In this foraminiferal succession five morphogroups were differentiated according to shell architecture (general shape, mode of coiling and number of chambers), integrated with the supposed microhabitat (epifaunal, shallow infaunal and deep infaunal) and feeding strategy (suspension-feeder, herbivore, bacterivore, etc.). The environmental evolution of the analysed section is interpreted by using the stratigraphic distribution of morphogroups, combined with species diversities and sedimentary data, in a sequence stratigraphic framework. The section comprises two depositional sequences, which demonstrate that species diversity and relative frequency of morphogroups are correlative with transgressive–regressive trends controlling depth and oxygenation of the water column. In both sequences, the maximum flooding interval is characterized by increased organic carbon content, dominance of the epifaunal morphogroups and reduced species diversity: features reflecting the increased degree of stagnation separating the transgressive phase from the regressive phase.  相似文献   

Global MHD Simulations of Space Plasma Environments: Heliosphere, Comets, Magnetospheres of Planets and Satellites     

K. Kabin  K.C. Hansen  T.I. Gombosi  M.R. Combi  T.J. Linde  D.L. DeZeeuw  C.P.T. Groth  K.G. Powell  A.F. Nagy 《Astrophysics and Space Science》2000,274(1-2):407-421

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A study of suprathermal oxygen atoms in Mars upper thermosphere and exosphere over the range of limiting conditions     

Arnaud Valeille  Michael R. Combi  Valeriy Tenishev  Stephen W. Bougher  Andrew F. Nagy 《Icarus》2010,206(1):18-27

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A comparison of global models for the solar wind interaction with Mars   总被引：1，自引：1，他引：0  

D. Brain  S. Barabash  S. Bougher  G. Chanteur  E. Dubinin  M. Fraenz  E. Harnett  E. Kallio  S. Ledvina  K. Liu  Y. Ma  A. Nagy  H. Nilsson  S. Simon 《Icarus》2010,206(1):139-151

We present initial results from the first community-wide effort to compare global plasma interaction model results for Mars. Seven modeling groups participated in this activity, using MHD, multi-fluid, and hybrid assumptions in their simulations. Moderate solar wind and solar EUV conditions were chosen, and the conditions were implemented in the models and run to steady state. Model output was compared in three ways to determine how pressure was partitioned and conserved in each model, the location and asymmetry of plasma boundaries and pathways for planetary ion escape, and the total escape flux of planetary oxygen ions. The two participating MHD models provided similar results, while the five sets of multi-fluid and hybrid results were different in many ways. All hybrid results, however, showed two main channels for oxygen ion escape (a pickup ion ‘plume’ in the hemisphere toward which the solar wind convection electric field is directed, and a channel in the opposite hemisphere of the central magnetotail), while the MHD models showed one (a roughly symmetric channel in the central magnetotail). Most models showed a transition from an upstream region dominated by plasma dynamic pressure to a magnetosheath region dominated by thermal pressure to a low altitude region dominated by magnetic pressure. However, calculated escape rates for a single ion species varied by roughly an order of magnitude for similar input conditions, suggesting that the uncertainties in both the current and integrated escape over martian history as determined by models are large. These uncertainties are in addition to those associated with the evolution of the Sun, the martian dynamo, and the early atmosphere, highlighting the challenges we face in constructing Mars’ past using models.  相似文献   

Regional disparities in Hungary during the period of transition to a market economy     

József Nemes Nagy 《GeoJournal》1994,32(4):363-368

Disparities in Hungary can be characterized regionally with the dualism of Budapest and the countryside, with the western and eastern division of the country itself, with local crises of the broken down industrial axis and marginal geographic settings, with the differentation according to the hierarchy and size of settlements. Two thirds of the total foreign capital invested in Hungary and half of the joint ventures are concentrated in the capital. Apart from Budapest, it causes a higher unemployment rate and lower taxable incomes.  相似文献