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Ebun Oni 《Pure and Applied Geophysics》1972,94(1):198-211
Summary The author proposes a new technique of magnetic interpretation in the case of a two-dimensional model, whereby six analytical expressions are deduced and computed forDH, DZ, PHB, PZB, AHB andAZB. These expressions denote the induced part of magnetic anomaly inH component, the induced part of anomaly inZ component, the permanent magnetization part ofH anomaly, the permanent magnetization part ofZ anomaly, the sum (DH+PHB), and the sum (DZ+PZB), respectively. The use of a series of these six curves taken together instead of the single profile curve, will improve the existing method of magnetic interpretation, reduce the uncertainties of the inverse problem, and provide a valuable tool for paleomagnetic studies of in situ older rocks commonly found in equatorial Africa. The resulting advantages outweigh the apparent increase in computation. This technique was applied to a field profile obtained across a subsurface dolerite vein, and the results agree with the theoretical predictions outlined. 相似文献
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Stephen K. Oni Martyn N. Futter Claudia Teutschbein Hjalmar Laudon 《Climate Dynamics》2014,42(9-10):2305-2321
Climate is an important driver of dissolved organic carbon (DOC) dynamics in boreal catchments characterized by networks of streams within forest-wetland landscape mosaics. In this paper, we assess how climate change may affect stream DOC concentrations ([DOC]) and export from boreal forest streams with a multi-model ensemble approach. First, we apply an ensemble of regional climate models (RCMs) to project soil temperatures and stream-flows. These data are then used to drive two biogeochemical models of surface water DOC: (1) The Integrated Catchment model for Carbon (INCA-C), a detailed process-based model of DOC operating at the catchment scale, and (2) The Riparian Integration Model (RIM), a simple dynamic hillslope scale model of stream [DOC]. All RCMs project a consistent increase in temperature and precipitation as well as a shift in spring runoff peaks from May to April. However, they present a considerable range of possible future runoff conditions with an ensemble median increase of 31 % between current and future (2061–2090) conditions. Both biogeochemical models perform well in describing the dynamics of present-day stream [DOC] and fluxes, but disagree in their future projections. Here, we assess possible futures in three boreal catchments representative of forest, mire and mixed landscape elements. INCA-C projects a wider range of stream [DOC] due to its temperature sensitivity, whereas RIM gives consistently larger inter-annual variation and a wider range of exports due to its sensitivity to hydrological variations. The uncertainties associated with modeling complex processes that control future DOC dynamics in boreal and temperate catchments are still the main limitation to our understanding of DOC mechanisms under changing climate conditions. Novel, currently overlooked or unknown drivers may appear that will present new challenges to modelling DOC in the future. 相似文献
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Adjacent catchments with similar patterns of land use and climate have markedly different dissolved organic carbon concentration and runoff dynamics 总被引：1，自引：0，他引：1 
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下载免费PDF全文 Temporal patterns in specific runoff, dissolved organic carbon concentrations [DOC] and fluxes were examined during two periods: 1994–1997 (period 1) and 2007–2009 (period 2) in five adjacent tributary catchments of Lake Simcoe, the largest lake in southern Ontario, Canada. The catchments displayed similar patterns of land use change with increases in urbanization (5–16%) and forest cover (0.2–4%) and declines in agriculture (4–8%) between 1994 and 2008. Climate in the catchments was similar; temperature increased slightly, but no significant change in precipitation was observed. Despite similar pattern of climate and land use, runoff responses and tributary [DOC] were different across the catchments. Following a very dry year (i.e. 1999), runoff increased steadily until the end of record. We observed increased variability in tributary [DOC] and higher DOC exports in period 2. This led to ~10% increase in [DOC] and a 13% increase in flux between the two study periods. Between the two periods, [DOC] increased by 15% in spring and 25% in summer, whereas flux increased by 17% in spring and 48% in summer. [DOC] was consistently higher in the growing (summer + autumn) than the dormant (winter + spring, minus spring melt months) seasons, but no unique pattern or simple linear flow/concentrations relationships existed. This suggests complex spatial and temporal pattern to runoff controls on DOC and flow dynamics in adjacent catchments. We therefore caution against extrapolating from monitored to unmonitored catchments. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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Ebun Oni 《Tectonophysics》1977,38(3-4)
Some deductions made from the magnetic anomaly profile of a body that had retained its strong negative permanent magnetization in the vertical field component, near the dip equator, has been utilized to supply information on a possible north—south shift of the western sector of the African plate. This constitutes a new approach to the tectonic physics of the African plate. 相似文献
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Hydrological footprints of urban developments in the Lake Simcoe watershed,Canada: a combined paired‐catchment and change detection modelling approach 下载免费PDF全文
下载免费PDF全文 Urban sprawl and regional climate variability are major stresses on surface water resources in many places. The Lake Simcoe watershed (LSW) Ontario, Canada, is no exception. The LSW is predominantly agricultural but is experiencing rapid population growth because of its proximity to the Greater Toronto area. This has led to extensive land use changes that have impacted its water resources and altered run‐off patterns in some rivers draining to the lake. Here, we use a paired‐catchment approach, hydrological change detection modelling and remote sensing analysis of satellite images to evaluate the impacts of land use change on the hydrology of the LSW (1994 to 2008). Results show that urbanization increased up to 16% in Lovers Creek, the most urban‐impacted catchment. Annual run‐off from Lovers Creek increased from 239 to 442 mm/year in contrast to the reference catchment (Black River at Washago) where run‐off was relatively stable with an annual mean of 474 mm/year. Increased annual run‐off from Lovers Creek was not accompanied by an increase in annual precipitation. Discriminant function analysis suggests that early (1992–1997; pre‐major development) and late (2004–2009; fully urbanized) periods for Lovers Creek separated mainly based on model parameter sets related to run‐off flashiness and evapotranspiration. As a result, parameterization in either period cannot be used interchangeably to produce credible run‐off simulations in Lovers Creek because of greater scatter between the parameters in canonical space. Separation of early and late‐period parameter sets for the reference catchment was based on climate and snowmelt‐related processes. This suggests that regional climatic variability could be influencing hydrologic change in the reference catchment, whereas urbanization amplified the regional natural hydrologic changes in urbanizing catchments of the LSW. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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This paper investigates the combined effect of small perturbations ε,ε′ in the Coriolis and centrifugal forces, radiation pressure q i , and changing oblateness of the primaries A i (t) (i=1,2) on the stability of equilibrium points in the restricted three body problem in which the primaries is a supergiant eclipsing binary system which consists of a pair of bright oblate stars having the appearance of a giant peanut in space and their masses assumed to vary with time in the absence of reactive forces. The equations of motion are derived and the equilibrium points are obtained. For the autonomized system, it is seen that there are more than a pair of the triangular points as κ→∞; κ being the arbitrary sum of the masses of the primaries. In the case of the collinear points, two additional equilibrium points exist on the line joining the primaries when simultaneously κ+ε′<0 and both primaries are oblate, i.e., 0<α i ?1. So there are five collinear equilibrium points in this case. Two non-planar equilibrium points exist for κ>1. Hence, there are at least nine equilibrium points of the system. The stability of these points is explored analytically and numerically. It is seen that the collinear and triangular points are stable with respect to certain conditions controlled by κ while the non-planar equilibrium points are unstable. 相似文献
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D. Onić 《Astrophysics and Space Science》2013,346(1):3-13
A considerable fraction of Galactic supernova remnants (SNRs) characterize flat spectral indices (α<0.5). There are several explanations of the flat radio spectra of SNRs in the present literature. The most of models involve a significant contribution of the second-order Fermi mechanism but some of them also discuss high compressions (>4), contribution of secondary electrons left over from the decay of charged pions, as well as the possibility of thermal contamination. In the case of expansion in high density environment, intrinsic thermal bremsstrahlung could theoretically shape the radio spectrum of an SNR and also account for observable curved—“concave up” radio spectra of some Galactic SNRs. This model could also shed a light on the question of flat spectral indices determined in some Galactic SNRs. On the other hand, present knowledge of the radio continuum spectra (integrated flux densities at different frequencies) of SNRs prevent definite conclusions about the significance of proposed models so the question on flat spectral indices still remains open. New observations, especially at high radio continuum frequencies, are expected to solve these questions in the near future. Finally, as there is a significant connection between the majority of Galactic SNRs with flat integrated radio spectrum and their detection in γ-rays as well as detection of radiative recombination continua in their X-ray spectra, the analysis of high energy properties of these SNRs is very important. 相似文献
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This paper investigates the stability of equilibrium points in the restricted three-body problem, in which the masses of the
luminous primaries vary isotropically in accordance with the unified Meshcherskii law, and their motion takes place within
the framework of the Gylden–Meshcherskii problem. For the autonomized system, it is found that collinear and coplanar points
are unstable, while the triangular points are conditionally stable. It is also observed that, in the triangular case, the
presence of a constant κ, of a particular integral of the Gylden–Meshcherskii problem, makes the destabilizing tendency of the radiation pressures
strong. The stability of equilibrium points varying with time is tested using the Lyapunov Characteristic Numbers (LCN). It
is seen that the range of stability or instability depends on the parameter κ. The motion around the equilibrium points L
i
(i=1,2,…,7) for the restricted three-body problem with variable masses is in general unstable. 相似文献