A method for the elimination of the compositional dependence of trace element distribution coefficients     

Roger L. Nielsen 《Geochimica et cosmochimica acta》1985,49(8):1775-1779

In an investigation of Sm, Sc, Sr, and Ti partitioning between diopside and silicate melt, Rayet al. (1983) showed that the compositional dependence of multicomponent exchange equilibria can not be eliminated by the application of the melt model of Bottinga and Weill (1972), and that the propagation of analytical error is an important contributor in the observed internal error in the calculated equilibria for those exchange reactions. We can demonstrate that the compositional dependence of single component distribution coefficients can be reduced below analytical error by the application of the two-lattice melt model first reported by Nielsenand Drake (1979) in a study of major element partitioning between pyroxene and melt. This model was later used for the calculation of major, minor and trace element partitioning by Nielsen and Dungan (1983). The two-lattice model is a modified version of the Bottinga-Weill model used by Drake (1976) for plagioclase-melt equilibria, and differs from that model in the assumed role of Al. The Nielsen and Dungan (1983) model has been modified here to assume Ti to mix in silicate melts as a network former. Single component distribution coefficients were used in place of multicomponent reactions in order to reduce the propagated analytical and experimental error.  相似文献   

Transient heat flow in a stratified medium     

Søren B. Nielsen  Niels Balling 《Tectonophysics》1985,121(1):1-10

The equation of heat conduction is solved for a horizontally stratified medium initially at constant temperature and subject to a step-function surface temperature change. The problem is solved by Laplace transformation and by applying a concept of further stratifications of the medium into unitary layers of constant ratio of thickness to the square root of thermal diffusivity. The solution takes the form of an infinite sum of complementary error functions, with coefficients given by recursion relations, is suitable for numerical applications and offers an attractive alternative to harmonic and quasi transient approaches in calculating the penetration of transient surface temperature variations into a layered medium. Use of the theorem of superposition yields a general expression for an arbitrary surface temperature function. The utility of the theory is illustrated by modelling examples of palaeoclimatically induced subsurface temperature and heat flow perturbations.  相似文献   

Is natrocarbonatite a cognate fluid condensate?     

Troels F. Nielsen  Ilya V. Veksler 《Contributions to Mineralogy and Petrology》2002,142(4):425-435

Natrocarbonatite flows in the crater of the volcano Oldoinyo Lengai (Tanzania) are the only carbonatite magmas observed to erupt and have provided strong arguments in favor of a magmatic origin for carbonatite. The currently favored explanation for the genesis of these carbonatites by liquid immiscibility between a silicate and a carbonatite melt is questioned based on the extremely low eruption temperatures of 544-593 °C and compositional and mineralogical characteristics not in agreement with experimental constraints. Experimental investigations of the relationship between Oldoinyo Lengai natrocarbonatite and related silicate rock compositions do indicate that alkali-bearing peralkaline carbonatite with liquidus calcite can form by liquid immiscibility. At the same time, these experiments result in evidence which speaks against a liquid immiscibility origin for the highly alkaline and peralkaline Oldoinyo Lengai natrocarbonatite. On the carbonatite side of the miscibility gap, fractional crystallization cannot account for a liquid evolution from alkali-bearing peralkaline carbonatite to highly alkaline natrocarbonatite. Such an evolution does not seem to be compatible with the liquidus mineral assemblages and the chemistry of Oldoinyo Lengai natrocarbonatite. No natural silicate magma is known to produce natrocarbonatite compositions by liquid immiscibility. The best interpretation of the Oldoinyo Lengai natrocarbonatite flows involves expulsion of a cognate, mobile, alkaline, and CO₂-rich fluid condensate. This conclusion is supported by recent studies of silicate and carbonatite melt inclusions in minerals of ultramafic alkaline complexes, trace element partitioning, isotopic constraints, and by experimental data on major element partitioning between coexisting H₂O-CO₂-rich fluid and carbonatitic melt. In contrast to all other suggested modes of formation, an origin of Oldoinyo Lengai natrocarbonatite from cognate fluid appears best to be in agreement with the field observations, the petrography, mineralogy, and geochemistry of Oldoinyo Lengai natrocarbonatite and the dynamics of the Oldoinyo Lengai natrocarbonatite extrusion.  相似文献   

Origin of upper-mantle seismic scattering – evidence from Russian peaceful nuclear explosion data     

Lars Nielsen  Hans Thybo  Alan Levander  Leonid N. Solodilov 《Geophysical Journal International》2003,154(1):196-204

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Similarity Scaling Of Surface-Released Smoke Plumes     

Torben Mikkelsen  Hans E. Jørgensen  Morten Nielsen  Søren Ott 《Boundary-Layer Meteorology》2002,105(3):483-505

Concentration fluctuation data from surface-layer released smokeplumes have been investigated with the purpose of finding suitable scaling parametersfor the corresponding two-particle, relative diffusion process.Dispersion properties have been measured at downwind ranges between 0.1 and 1 km from a continuous, neutrally buoyant ground level source. A combinationof SF₆ and chemical smoke (aerosols) was used as tracer. Instantaneous crosswind concentration profiles of high temporal (up to 55 Hz) and spatialresolution (down to 0.375 m) were obtained from aerosol-backscatter Lidar detectionin combination with simultaneous gas chromatograph (SF₆) reference measurements. The database includes detailed crosswind concentration fluctuation measurements. Each experiment, typically of 1/2-hour duration, containsplume mean and variance concentration profiles, intermittency profiles andexceedence and duration statistics. The diffusion experiments were accompanied by detailed in-situ micrometeorological mean and turbulence measurements. In this paper, a new distance-neighbour function for surface-released smoke plumes is proposed, accompanied by experimental evidence in its support. The new distance-neighbour function is found to scale with the surface-layer friction velocity,and not with the inertial subrange dissipation rate, over the range of distance-neighbour separations considered.  相似文献   

Discussion of Gabrielsen et al. (2010): Latest Caledonian to Present tectonomorphological development of southern Norway     

S.B. Nielsen  O.R. Clausen  V.K. Pedersen  J.-E. Leseman  B. Goledowski  M. Huuse  K. Gallagher  M.A. Summerfield 《Marine and Petroleum Geology》2010

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И-Shaped surf beat understood in terms of transient forced long waves     

Peter Nielsen  Tom E. Baldock 《Coastal Engineering》2010

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How storm size matters for surge height     

Peter Nielsen 《Coastal Engineering》2009

The observed trend of peak storm surge η_max increasing with storm size R_max, roughly as η_max ∞ R_max^0.22, particularly on gently sloping coasts, is discussed in relation to the simple 1D analytical solutions for forced long waves due to respectively surface pressure p_s and wind stress τ_w. At constant depth h, the τ_w-driven surge is proportional to storm size while the p_s-driven part is not. This could perhaps be seen to explain why the size-dependence is stronger on flatter slopes where the τ_w-driven surge dominates. However, this direct size dependence disappears in the sloping beach scenario if the typical depth is assumed proportional to storm size. The observed size dependence is then more likely due to a combination of two 2D effects: Firstly, the sideways radiation from a travelling surge which exceeds the “stationary height” Δ_p/ρg is relatively weaker for a wider system. Secondly, the wind stress field is a dipole, and the mutual cancellation of the two poles is weaker for larger systems.  相似文献   

Kerogen model breakdown: Comments to Lerche (1991) and Liu and Lerche (1990)     

Soren B. Nielsen  Alan K. Burnham 《Mathematical Geology》1993,25(1):81-89

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The geography of pastoral mobility: A spatio-temporal analysis of GPS data from Sahelian Senegal     

Hanne Kirstine Adriansen  Thomas Theis Nielsen 《GeoJournal》2005,64(3):177-188

The aim of this paper is to show the contribution of geography to the study of pastoral mobility. While pastoralists of Ferlo, Senegal, have become semi-sedentary, little is known about the mobility of their livestock. In this paper, pastoral mobility is analysed using GPS measurements of cattle movements made by a pastoralist from 1997 to 2000. Based on data from 3 years, a quantification of the extent of movements and mappings of the patterns are made. The results show that cattle walk about 5000 km on an annual basis, and while a great deal of the mobility can be characterised as daily circular movements between the camp and watering points, occasional transhumance is still used to make the most of variable resources.  相似文献