Computer studies of the evolution of planetary and satellite systems     

Nils Aall Barricelli  Kjell Aashamar 《Earth, Moon, and Planets》1980,22(4):385-417

This paper describes two computer experiments carried out with a CDC-Cyber 74 program (Barricelliet al., 1979) for computer simulation of a large number of objects in orbit about a central body or primary. The first experiment was started with 125 planets of which the two largest ones had coplanar orbits and masses comparable to those of Jupiter and Saturn, respectively. Their semimajor axes and eccentricities were, however, much larger. The smaller planets had a distribution promoting the formation of an axial meeting area. The experiment gives information relevant to the question of focusing of planetary orbits into a common plane and to the question of the formation and stability of an axial meeting area. Together with the next experiment, it also gives information about the development of commensurabilities (or resonances) with the largest planets.The second experiment started with 55 planets none of them with a mass greater than about 20% of Jupiter's but several of them with orbits close to a common plane. The aim of the experiment was to investigate whether successive captures followed by planetary fusion (Barricelli, 1972a) could lead to the formation of major planets comparable to Jupiter and Saturn, and in similar orbits. Also this experiment gives information relevant to the commensurability problem.  相似文献   

Interpretation of grazing impacts on Mars by the axial rotation theory     

Nils Aall Barricelli 《Earth, Moon, and Planets》1984,31(1):75-78

This paper calls attention to the fact that the distribution of grazing impacts on Mars, as described by Schultz and Lutz-Garihan (1982), agrees with the distribution predictable by the theory of planetary axial rotation based on the transmission of mass and angular momentum from a satellite system to its primary (Barricelli, 1972). A few additional implications of the theory are pointed out.  相似文献   

Alpine Activity Patterns of Mitopus morio （Fabricius, 1779） are Induced by Variations in Temperature and Humidity at Different Scales in Central Norway     

Nils HEIN  ;Roland PAPE  ;Oliver-D. FINCH  ;Jorg LOFFLER 《山地科学学报》2014,11(3):644-655

Our research addresses questions about how micro-climate affects activity abundance of a common and widespread harvestman in an alpine ecosystem. Activity patterns of the Harvestman Mitopus morio （Fabricius, 1779） were studied along different alpine gradients in the central Norwegian Scandes. Within a nested design, we surveyed 18 alpine habitats with pitfall traps and microclimatological equipment along oceanic-continental, two elevational, and （fine-scaled） microtopographic gradients. Sites in the oceanic region of the Scandes showed generally higher abundance of M. morio than sites in the continental region. Furthermore, along the elevational gradient, middle-alpine sites showed higher abundances than low-alpine sites. These general patterns are best explained by higher humidity in the oceanic region and in the middlealpine belt. Focusing at a finer scale, i.e. one elevational level within each region, revealed partly opposing activity patterns within relatively short distances. While in the western middle-alpine belt these patterns were best explained by humidityrelated measures but now with higher activity abundance during drier conditions, in the drier eastern middle-alpine belt heat sums rather than humidity were found to be the best explanatoryvariables for the observed patterns. Hence, our results imply a pronounced different reaction of the two populations towards climatic variables that partly even contradict the previously described general pattern. Regardless whether these differences in activity abundance in M. morio are a form of phenotypic plasticity or adaptation, our findings stress the importance of detailed autecological knowledge combined with fine-scaled climatic measurements when aiming at predictions about possible future ecosystem structures and spatiotemporal phenomena. M. morio proves to be an ideal biogeographic model organism for understanding spatio-temporal responses of alpine ecosystems under modified climatic conditions.  相似文献   

Towards a Higher Comparability of Geothermometric Data obtained by Raman Spectroscopy of Carbonaceous Material. Part I: Evaluation of Biasing Factors   总被引：1，自引：0，他引：1  

Nils K. Lünsdorf  Istvan Dunkl  Burkhard C. Schmidt  Gerd Rantitsch  Hilmar von Eynatten 《Geostandards and Geoanalytical Research》2014,38(1):73-94

Raman spectroscopy of carbonaceous material (RSCM) is frequently used to determine metamorphic peak temperatures from the structural order of carbonaceous material enclosed in metasediments. This method provides a quick, robust and relatively cheap geothermometer. However, the comparability of the RSCM parameter is low as there are at least three major sources of biasing factors. These sources are the spectral curve‐fitting procedure, the sample characteristics itself and the experimental design including the used Raman system. To assess the impacts of the biasing factors on RSCM, a series of experiments was performed. The experiments showed that curve‐fitting is strongly influenced by individual operator‐bias and the degrees of freedom in the model, implying the need for a standardised curve‐fitting procedure. Due to the diversity of components (optics, light detection device, gratings, etc.) and their combinations within the Raman systems, different Raman instruments generally give differing results. Consequently, to estimate comparable metamorphic temperatures from RSCM data, every Raman instrument needs its own calibration. This demands a reference material series that covers the entire temperature calibration range. Although sample heterogeneity will still induce some variation, a reference material series combined with standardised curve‐fitting procedures will significantly increase the overall comparability of RSCM data from different laboratories.  相似文献   

Nitrogen Retention in Coastal Marine Sediments—a Field Study of the Relative Importance of Biological and Physical Removal in a Danish Estuary     

Søren Laurentius Nielsen  Nils Risgaard-Petersen  Gary T. Banta 《Estuaries and Coasts》2017,40(5):1276-1287

The aim of this study was to elucidate the relative importance of physical versus biological loss processes for the removal of microphytobenthic (MPB) bound nitrogen in a coastal environment at different times of the year via a dual isotope labeling technique. We used ⁵¹Cr, binding to inorganic sediment particles but not participating in any biological processes, and ¹⁵N–NO₃ ^?, taken up by the MPB and turned over as part of the MPB nitrogen pool. Retention, down-mixing, and export of ¹⁵N were due to both biological and physical processes, so that by comparing retention of the two isotopes, we were able to discern the relative importance of physical and biological processes. The isotope marking was supplemented with measurements of sediment chlorophyll biomass and oxygen fluxes, allowing us to evaluate MPB biomass as well as primary production vs. respiration in the sediment. In spring/early summer, the system was characterized by tight N cycling and high N retention: any remineralized N was immediately taken up and retained in the MPB biomass. In late summer and autumn, the system was still physically stable, but high biological mediated N losses were observed. In early winter, the system was physically dominated due to low MPB biomasses and activity combined with a significant storm event. Our data support the hypothesis that the relative balance between physical and biological processes in determining retention and removal of MPB-bound nitrogen changes seasonally.  相似文献   

Induction studies with satellite data   总被引：2，自引：0，他引：2  

Nils Olsen 《Surveys in Geophysics》1999,20(3-4):309-340

The natural variations of the Earth's magnetic field of periods spanning from milliseconds to decades can be used to infer the conductivity-depth profile of the Earth's interior. Satellites provide a good spatial coverage of magnetic measurements, and forthcoming missions will probably allow for observations lasting several years, which helps to reduce the statistical error of the estimated response functions.Two methods are used to study the electrical conductivity of the Earth's mantle in the period range from hours to months. In the first, known as the potential method, a spherical harmonic analysis of the geomagnetic field is performed, and the Q-response, which is the transfer function between the internal (induced) and the external (inducing) expansion coefficients is determined for a specific frequency. In the second approach, known as the geomagnetic depth sounding method, the C-response, which is the transfer function between the magnetic vertical component and the horizontal derivative of the horizontal components, is determined. If one of these transfer functions is known for several frequencies, models of the electrical conductivity in the Earth's interior can be constructed.This paper reviews and discusses the possibilities for induction studies using high-precision magnetic measurements from low-altitude satellites. The different methods and various transfer functions are presented, with special emphasis on the differences in analysing data from ground stations and from satellites. The results of several induction studies with scalar satellite data (from the POGO satellites) and with vector data (from the Magsat mission) demonstrate the ability to probe the Earth's conductivity from space. However, compared to the results obtained with ground data the satellite results are much noisier, which presumably is due to the shorter time series of the satellite studies.The results of a new analysis of data from the Magsat satellite indicate higher resistivity in oceanic areas than in continental areas. However, since this holds for the whole range of periods between 2 and 20 days, this difference probably is not caused purely by differences in mantle conductivity (for which one would expect less difference for the longer periods). Further studies with data from recently launched and future satellites are needed.  相似文献   

3D CFD MODELING OF WATER AND SEDIMENT FLOW IN A HYDROPOWER RESERVOIR     

Nils Reidar B.OLSEN  Oscar F.JIMENEZ  Lars ABRAHAMSEN  and Aslak L*IVOLL 《国际泥沙研究》1999,(1)

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A simple approach to adjust tidal forcing in fjord models     

Karina Hjelmervik  Nils Melsom Kristensen  André Staalstrøm  Lars Petter Røed 《Ocean Dynamics》2017,67(7):949-958

To model currents in a fjord accurate tidal forcing is of extreme importance. Due to complex topography with narrow and shallow straits, the tides in the innermost parts of a fjord are both shifted in phase and altered in amplitude compared to the tides in the open water outside the fjord. Commonly, coastal tide information extracted from global or regional models is used on the boundary of the fjord model. Since tides vary over short distances in shallower waters close to the coast, the global and regional tidal forcings are usually too coarse to achieve sufficiently accurate tides in fjords. We present a straightforward method to remedy this problem by simply adjusting the tides to fit the observed tides at the entrance of the fjord. To evaluate the method, we present results from the Oslofjord, Norway. A model for the fjord is first run using raw tidal forcing on its open boundary. By comparing modelled and observed time series of water level at a tidal gauge station close to the open boundary of the model, a factor for the amplitude and a shift in phase are computed. The amplitude factor and the phase shift are then applied to produce adjusted tidal forcing at the open boundary. Next, we rerun the fjord model using the adjusted tidal forcing. The results from the two runs are then compared to independent observations inside the fjord in terms of amplitude and phases of the various tidal components, the total tidal water level, and the depth integrated tidal currents. The results show improvements in the modelled tides in both the outer, and more importantly, the inner parts of the fjord.  相似文献