The Ituwa Surge deposits of the Holocene Ngozi caldera,Mbeya Region,Tanzania     

Nils Lenhardt  Gert-Jan Peeters  Athanas S. Macheyeki 《International Journal of Earth Sciences》2015,104(3):749-751

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Mach number dependence of the onset of dynamo action     

Nils Erland L. Haugen  Axel Brandenburg  Antony J. Mee 《Monthly notices of the Royal Astronomical Society》2004,353(3):947-952

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A toy model for global magnetar oscillation     

Kostas Glampedakis  Lars Samuelsson  Nils Andersson 《Astrophysics and Space Science》2007,308(1-4):607-611

The presence of a magnetic field in a neutron star interior results in a dynamical coupling between the fluid core and the elastic crust. We consider a simple toy-model where this coupling is taken into account and compute the system’s mode oscillations. Our results suggest that the notion of pure torsional crust modes is not useful for the coupled system, instead all modes excite Alfvén waves in the core. However, we also show that among a rich spectrum of global MHD modes the ones most likely to be excited by a fractured crust are those for which the crust and the core oscillate in concert. For our simple model, the frequencies of these modes are similar to the “pure crustal” frequencies. We advocate the significant implications of these results for the attempted theoretical interpretation of QPOs during magnetar flares in terms of neutron star oscillations.   相似文献   

Terrestrial carbon-isotope records from coastal deposits (Algarve, Portugal): a tool for chemostratigraphic correlation on an intrabasinal and global scale     

Ulrich Heimhofer  Peter A. Hochuli  Stefan Burla  Nils Andersen  Helmut Weissert 《地学学报》2003,15(1):8-13

ABSTRACT The carbon-isotope signature of terrestrial organic matter (OM) offers a valuable tool to develop stratigraphic correlations for near-shore deposits. A mid-Cretaceous coastal succession of the western Algarve Basin, Portugal, displays a marked negative δ¹³C excursion ranging from − 21.2‰ to − 27.8‰ in the Early Aptian followed by two shifts towards higher values (up to − 19.3‰) during the Early and Late Aptian, respectively. The dominance of cuticle and leaf debris in the bulk OM fraction is confirmed by optical studies, Rock-Eval pyrolysis and by comparison with the δ¹³C signature of four different types of fossilized land-plant particles. Correlation of two terrestrial δ¹³C_bulk OM records from different study sites leads to a significant enhancement of the intrabasinal stratigraphic correlation within the Algarve Basin. Three prominent excursions in the Portuguese records can be correlated with existing δ¹³C curves from pelagic and terrestrial environments. The general carbon-isotope pattern is superimposed by small-scale fluctuations which can be explained by compositional variations within the OM.  相似文献   

Reconstruction of Middle to Late Quaternary sea level using submerged speleothems from the northeastern Yucatán Peninsula     

Simon D. Steidle  Sophie F. Warken  Nils Schorndorf  Julius Förstel  Andrea Schröder-Ritzrau  Gina E. Moseley  Christoph Spötl  Jeronimo Aviles  Wolfgang Stinnesbeck  Norbert Frank 《第四纪科学杂志》2021,36(7):1190-1200

We examined 14 subaerially deposited speleothems retrieved from submerged caves in the northeastern Yucatán Peninsula (Mexico). These speleothems grew during the Middle to Late Quaternary and were dated by ²³⁰Th-U techniques to provide upper depth limits for past sea levels. We report the first relative sea-level limits for Marine Isotope Stages (MIS) 11 and 6, and present new evidence for sea-level oscillations during MIS 5 and early MIS 1. For the latter periods, the origin of growth interruptions is evaluated by combining petrographic methods with trace element analyses. The MIS 5c sea-level highstand probably occurred between 103.94 ± 0.58 ka and 96.82 ± 0.42 ka and must have exceeded -10.8 m (relative to present-day local sea level). The minimum average rate of sea-level fall over a 9.4 ka-long period during the MIS 5e/5d transition is calculated from stalagmite and published coral data at 1.74 ± 0.37 m/ka. For the early Holocene, previous discrepancies with respect to a potential multimetre oscillation of local sea level were found to be challenging to reconcile with the existing speleothem data from the area.  相似文献   

Utilisation of the lunar field for interplanetary travel by the Oslo system     

Nils Aall Barricelli  Ove Havnes  Erik Bølviken 《Earth, Moon, and Planets》1971,2(4):468-473

This paper presents preliminary results of orbital investigations by a data processing machine aimed at the utilisation of the lunar gravitational field in interplanetary travel. The lunar field is utilised in two successive steps. In the first step a spacecraft in an Earth-bound orbit is deviated into an orbit similar to but separated from the Earth's orbit around the Sun. In a successive approach between the spacecraft and the Earth-Moon system the combined fields of the Earth and the Moon are utilised as a means to convey to the spacecraft a main portion of the momentum required in order to carry it to the proximity of Venus.A substantial portion of the fuel required for space travel can be saved by this kind of procedure.The CD 3300 machine time needed for this investigation was supplied by the computing facility of the University of Oslo at Blindern.  相似文献   

The influence of selenium on photosynthesis and "light-enhanced dark respiration" (LEDR) in the flagellate Euglena gracilis after exposure to ultraviolet radiation     

Nils G.A. Ekelund  Roman A. Danilov 《Aquatic Sciences - Research Across Boundaries》2001,63(4):457-465

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Sensitivity of last glacial maximum climate to sea ice conditions in the Nordic Seas     

Øyvind Byrkjedal  Nils Gunnar Kvamstø  Marius Meland  Eystein Jansen 《Climate Dynamics》2006,26(5):473-487

Published reconstructions of last glacial maximum (LGM) sea surface temperatures and sea ice extent differ significantly. We here test the sensitivity of simulated North Atlantic climates to two different reconstructions by using these reconstructions as boundary conditions for model experiments. An atmospheric general circulation model has been used to perform two simulations of the (LGM) and a modern-day control simulation. Standard (CLIMAP) reconstructions of sea ice and sea surface temperatures have been used for the first simulation, and a set of new reconstructions in the Nordic Seas/Northern Atlantic have been used for the second experiment. The new reconstruction is based on 158 core samples, and represents ice-free conditions during summer in the Nordic Seas, with accordingly warmer sea surface temperatures and less extensive sea ice during winter as well. The simulated glacial climate is globally 5.7 K colder than modern day, with the largest changes at mid and high latitudes. Due to more intense Hadley circulation, the precipitation at lower latitudes has increased in the simulations of the LGM. Relative to the simulation with the standard CLIMAP reconstructions, reduction of the sea ice in the North Atlantic gives positive local responses in temperature, precipitation and reduction of the sea level pressure. Only very weak signatures of the wintertime Icelandic Low occur when the standard CLIMAP sea surface temperature reconstruction is used as the lower boundary condition in LGM. With reduced sea ice conditions in the Nordic Seas, the Icelandic Low becomes more intense and closer to its present structure. This indicates that thermal forcing is an important factor in determining the strength and position of the Icelandic Low. The Arctic Oscillation is the most dominant large scale variability feature on the Northern Hemisphere in modern day winter climate. In the simulation of the LGM with extensive sea ice this pattern is significantly changed and represents no systematic large scale variability over the North Atlantic. Reduction of the North Atlantic sea ice extent leads to stronger variability in monthly mean sea level pressure in winter. The synoptic variability appears at a lower level in the simulation when standard reconstructions of the sea surface in the LGM are used. A closer inspection of storm tracks in this model experiment shows that that the synoptic lows follow a narrow band along the ice edge during winter. The trajectories of synoptic lows are not constrained to the sea ice edge to the same degree when the sea ice extent is reduced. Seasonally open waters in the Nordic Seas in the new reconstruction apparently act as a moisture source, consistent with the current understanding of the rapid growth of the Fennoscandian and Barents Ice Sheets, during the LGM. The signal from the intensified thermal forcing in the North Atlantic in Boreal winter is carried zonally by upper tropospheric waves, and thus generates non-local responses to the changed sea ice cover.  相似文献   

Towards gravitational wave asteroseismology     

Nils Andersson  & Kostas D. Kokkotas 《Monthly notices of the Royal Astronomical Society》1998,299(4):1059-1068

We present new results for pulsating neutron stars. We have calculated the eigenfrequencies of the modes that one would expect to be the most important gravitational wave sources: the fundamental fluid f mode, the first pressure p mode and the first gravitational wave w mode, for twelve realistic equations of state. From these numerical data we have inferred a set of 'empirical relations' between the mode frequencies and the parameters of the star (the radius R and the mass M ). Some of these relations prove to be surprisingly robust, and we show how they can be used to extract the details of the star from observed modes. The results indicate that, should the various pulsation modes be detected by the new generation of gravitational wave detectors that come online in a few years, the mass and the radius of neutron stars can be deduced with errors no larger than a few per cent.  相似文献   

Species richness and environmental conditions of fish along the Norwegian Skagerrak coast     

Lekve  Kyrre; Stenseth  Nils Chr.; Gjosaeter  Jakob; Doledec  Sylvain 《ICES Journal of Marine Science》2002,59(4):757-769

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