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1.
A new method is described for estimating: (a) the meridional electric current density, jθ, (b) the vertical growth rate of the zonal magnetic field, ∂Bφ/∂r, or its scale-height, Bφ/∂Bφ/∂r) and (c) the vertical growth rate of the vertical current density, ∂jr/∂r, at a few isolated points on the top surface of the Earth's core from observations of the internal geomagnetic field at the Earth's surface. The theoretical technique rests on combining unaccelerated, gravitationally-driven Boussinesq fluid dynamics of the core with frozen-flux electromagnetism, the mantle being treated as a spherically symmetric insulator.
Insertion into this theory of main field models for epochs 1965, 1975 leads to preliminary values for these quantities of magnitude: (a) jθ 1 A/m2, (b) ∂Bφ/∂r 10−6 T/m or Bφ/(∂Bφ/∂r) 10 m, (c) ∂jr/∂r 10−6 A/m3. Some geophysical implications of these estimates are discussed. 相似文献
2.
Elodie Salmon Adri C.T. van Duin François Lorant Paul-Marie Marquaire William A. Goddard 《Organic Geochemistry》2009,40(3):416-427
This paper reports ReaxFF MD simulation results on pyrolysis of a molecular model of the algaenan Botryococcus braunii race L biopolymer, specifically, ReaxFF predictions on the pyrolysis of prototypical chemical structures involving aliphatic chain esters and aldehydes. These preliminary computational experiments are then used to analyze the thermal cracking process within algaenan race L biopolymers. The simulations indicate that the thermal decomposition of the algaenan biopolymer is initiated by the cleavage of a C–O bond in the ester group, followed by the release of carbon dioxide. We also observe a significant, strongly temperature dependent, release of ethylene. This degradation mechanism leads to products similar to those observed in pyrolysis experiments, validating this computational approach. 相似文献
3.
Elodie Salmon Françoise Behar François Lorant Patrick G. Hatcher Paul-Marie Marquaire 《Organic Geochemistry》2009,40(4):500-509
We have developed a theoretical approach for evaluating the maturation of kerogen-like material, involving molecular dynamic reactive modelling with a reactive force field to simulate thermal stress. Morwell Brown Coal was selected to study the thermal evolution of terrestrial organic matter (OM). To achieve this, a structural model is first constructed on the basis of literature models and analytical characterization of our samples using modern 1and 2D nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FTIR) spectroscopy and elemental analysis. Then, artificial maturation of the coal is performed at low conversion in order to obtain quantitative and qualitative detailed evidence for the structural evolution of the kerogen upon maturation. The chemical changes include defunctionalization of carboxyl, carbonyl and methoxy functional groups, coupled with an increase in cross linking in the residual matured kerogen. Gaseous and liquid hydrocarbons, essentially CH4, C4H8 and C14+ hydrocarbons, are generated in low amount, merely via cleavage of the lignin side chain. 相似文献
4.
Elodie Salmon Françoise Behar François Lorant Patrick G. Hatcher Pierre Metzger Paul-Marie Marquaire 《Organic Geochemistry》2009,40(3):400-415
The thermal reactivity of organic matter in source rocks is usually kinetically represented by a set of parallel and independent first order reactions. The approach assumes that only defunctionalisation reactions take place upon thermal decomposition, regardless of the chemical nature of kerogen. We have developed a new method for evaluating maturation pathways for an important kerogen-forming geopolymer, algaenan from the alga Botryococcus braunii (B. braunii), involving molecular dynamic reactive modelling based on quantum mechanics to reproduce maturation. To achieve this, a structural model is first constructed on the basis of models from the literature and analytical characterization of our samples using modern 1D and 2D nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FTIR) and elemental analysis (EA). Then, thermal decomposition of the algaenan is performed at low conversion in order to describe the initial transformations analytically. In an additional step, the observed chemical changes are quantitatively and qualitatively compared to simulated maturation from the molecular models. From this simulated maturation detailed reaction schemes are extracted for primary cracking mechanisms. 相似文献
5.
Alterations in topography due to the construction of transport infrastructure and industrial development are the results of rather complex processes. The impact of transport constructions upsetting (topographic) equilibrium is manifested in a relatively narrow strip, and, mostly, through producing abnormally steep slopes, in reducing relief stability. The earthworks for transport routes are themselves also landscape-forming factors whereas in the case of industrial developments, planation is usually mentioned. Topographic changes related to the construction of transport infrastructure and industrial development are discussed historically in this chapter. Among the direct impacts of the first are those related to the construction of Roman and Medieval roads, hollow roads in loess, public roads, motorways, railways, canals, tunnels and airports; while of the second are those of early mining and metallurgy, cellars, sludge reservoirs, slag cones and fly-ash reservoirs, cooling ponds, industrial parks, shopping centres and waste disposal sites. Of the indirect ones, an introduction is given to impacts of surface sealing, changes in runoff, the ‘waterfall effect,’ as well as to environmental impacts under permafrost conditions. 相似文献
6.
Lorant A. Muth 《Physics of the Earth and Planetary Interiors》1979,20(2-4):119-123
The ground state of the core-mantle conductivity system is defined as a step function transition from the constant non-zero conductivity of the core to zero conductivity in the mantle. This ground state is reached by letting the thickness of a transition region Δ → 0, where Δ appears as a parameter in the model conductivity of the system. By a transformation of the equation governing the behavior of the electrostatic potential φ, it is shown that the function V(x) = (1/σ1/2)(d2σ1/2/dx2) acts as a potential barrier in the quantum mechanical sense, and that for certain conductivity profiles σ(x), where x is the usual Cartesian coordinate, the electrostatic potential is screened out in regions where σ(x) → 0 as Δ → 0. Consequently, E = −φ also vanishes in these regions. The results generalize to the time-dependent case. Conditions that the conductivity function σ(x) must satisfy to qualify as the ground-state conductivity are defined and an example is provided. 相似文献
7.
The time histories of the emission at 10, 30, and 100 keV averaged over the loop from small and large loop thermal models of hard X-ray emission are studied. The small (15000 km) loop cases show a characteristic delay in the peak of the 100 keV emission relative to the 30 keV emission of about 1.5 s which should be detectable. The large (47 000 km) loop cases show no delay, but in the case of a continuous energy input, the 30 keV emission has a peak at 9.5 s whereas the 100 keV emission rises monotonically. Again, this difference should be detectable to the extent that it is not washed out by a dominant beam or escaping tail component which is not considered in this paper. A large loop case where only classical and saturated heat conduction are allowed is considered. The 30 keV emission has a peak at 7.5 s whereas the 100 keV emission rises monotonically. The peak temperature reached is 8 × 107 K and the probability of finding examples in the data uncontaminated by a dominant beam or escaping tail component should be considerably higher than in the cases with higher rates of energy input. 相似文献
8.
An expression for the inviscid horizontal velocity field at the surface of the Earth's core necessary to account for the poloidal main magnetic field and its secular variation seen at the Earth's surface is derived for an insulating mantle in the limit of infinite core conductivity. The starting point of derivation is Ohm's law rather than the magnetohydrodynamic induction equation. Maps of the resulting motion for epoch 1965.0 at different truncation levels are presented and discussed. 相似文献
9.
10.
The present study investigates the sensitivity of the frequency distribution of precipitation rates to the closure employed
in the penetrative mass flux cumulus parameterization of Zhang and McFarlane in the Canadian regional climate model (CRCM)
and in the Canadian Centre for Climate Modelling and Analysis third generation global atmospheric general circulation model
(AGCM3). The effects of an alternative prognostic closure for mass flux cumulus parameterization in place of the original
diagnostic closure are investigated. A set of experiments is performed in which changes in the frequency distribution of precipitation
rates and cloud base mass-flux are examined as a function of the parameters that define each closure scheme. The relationship
between the frequency distribution of precipitation and cloud base mass flux is examined and a self-consistent relation is
found when the depth of convection is taken into account. Experiments performed with the prognostic closure favor relatively
strong cloud base mass-flux and deep penetrative convection with relatively more intense convective precipitation. The mean
of the frequency distribution of convective precipitation is larger and the heavier events become more intense. Also, experiments
performed with the prognostic closure favor less frequent convective activity. However these changes in the distribution of
convective component of precipitation are generally offset by opposite changes in the distribution of the resolved large-scale
component of precipitation, resulting in relatively smaller changes in total precipitation. The altered partition of precipitation
between convective and large-scale components is found to alter the energy balance and the thermodynamic equilibrium structure
of the troposphere. The robustness found in the CRCM results regarding the sensitivity of the frequency distribution of precipitation
to changes in the closure of the deep convection parameterization is investigated by performing a similar analysis of AGCM3
simulations. A remarkable similarity of AGCM3 and CRCM results is found suggesting that the closure sensitivity identified
in this study is robust. 相似文献