共查询到20条相似文献，搜索用时 31 毫秒
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Alvin L. Bradshaw Peter G. Brewer Deborah K. Shafer Robert T. Williams 《Earth and Planetary Science Letters》1981,55(1):99-115
Approximately 6000 determinations of the alkalinity and total carbon dioxide content of seawater have now been made in the Atlantic, Pacific and Indian Oceans as part of the GEOSECS program by a computer-controlled potentiometric titration technique. The equations used to locate the equivalence points of the carbonic acid system on this titration curve were developed in 1971 but have not previously been published. These functions may be represented by:Upon inspection, these functions are analogous to the modified Gran functions of Hansson and Jagner [25] with the omission of the contributions of [OH?] and [CO32?], and with the contribution of B(OH)4? being assessed at a chlorinity of 19‰ for all samples. Reprocessing the original titration e.m.f.-volume data with appropriate corrections and modified Gran functions reveals an error of about +12 μmol/kg in the GEOSECS total carbon dioxide data. In addition, the protonation of dissolved phosphate species during the titration results in a contribution to measured total carbon dioxide equal to the total phosphate concentration. Differences in the application of the GEOSECS functions between the Atlantic and the Pacific-Indian Oceans expeditions are also to be found so that the error deriving from this source for the Atlantic expedition was only +5 μmol/kg. The application of the correct functions increases precision enabling smaller differences, such as those attributable to fossil fuel carbon dioxide, potentially to be observed, and increases accuracy so that the error in titrator total carbon dioxide previously diagnosed by Takahashi [14] can be logically accounted for. 相似文献
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It is important to examine the ratio of measured to total sediment discharge to determine the error in measured sediment transport rates from depth-integrated samplers. The ratio of measured to total sediment discharge as well as the ratio of suspended to total sediment discharge are examined based on the Modified Einstein Procedure. Both ratios reduce to a function of the ratio of shear velocity, , to the fall velocity, , of suspended material, , and the ratio, , of flow depth, h, to the median grain size of bed material, . In rivers transporting fine material (such as silt or clay), the ratio of suspended to total load is a function of the ratio, . In this study, it is found that the ratio of measured to total load becomes a simple function of flow depth. For fine sediment transport, with a Rouse number (Ro) , at least 80% of sediment load is in suspension when , and at least 90% of sediment load is measured from depth integrating samples when . Detailed measurements from 35 river stations in South Korea demonstrate that sand sizes and finer fractions predominantly are transported in suspension. Also, at least 90% of sand and finer fractions are transported in suspension in gravel and sand bed rivers when the discharge is larger than the mean annual discharge. 相似文献
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One-dimensional flows of gravity currents within horizontal and inclined porous channels are investigated combining theoretical and experimental analysis to evaluate the joint effects of channel shape and fluid rheology. The parameter governs the shape of the channel cross section, while the fluid rheology is characterised by a power-law model with behaviour index n. Self-similar scalings for current length and height are obtained for horizontal and inclined channels when the current volume increases with time as .For horizontal channels, the interplay of model parameters , and governs the front speed, height, and aspect ratio of the current (ratio between the average height and the length). The dependency is modulated by two critical values of and . For all channel shapes, discriminates between currents whose height decreases () or increases () with time at a particular point. For all power-law fluids, discriminates between decelerated currents, with time-decreasing aspect ratio (), and accelerated currents, with time-increasing aspect ratio (). Only currents with time-decreasing height () and aspect ratio () respect model assumptions asymptotically; the former constraint is more restrictive than the latter.For inclined channels, a numerical solution in self-similar form is obtained under the hypothesis that the product of the channel inclination and the slope of the free-surface is much smaller than unity; this produces a negligible error for , and is acceptable for . The action of gravity in inclined channels is modulated by both the behaviour index n and the shape factor . For constant flux, the current reaches at long times a steady state condition with a uniform thickness profile. In steep channels and for sufficiently long currents, the free-surface slope becomes entirely negligible with respect to channel inclination, and the constant thickness profile depends only on n.Theoretical results are validated by comparison with experiments (i) in horizontal and inclined channels with triangular or semicircular cross-section, (ii) with different shear-thinning fluids, and (iii) for constant volume and constant flux conditions. The experimental results show good agreement with theoretical predictions in the long-time regime.Our analysis demonstrates that self-similar solutions are able to capture the essential long-term behaviour of gravity currents in porous media, accounting for diverse effects such as non-Newtonian rheology, presence of boundaries, and channel inclination. This provides a relatively simple framework for sensitivity analysis, and a convenient benchmark for numerical studies. 相似文献
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《Continental Shelf Research》2007,27(10-11):1447-1464
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This paper proposes a novel strategy for the investigation of displacement amplitude () near and along an oblique-truncated semicircular canyon subjected to shear horizontal (SH) waves. Transfinite interpolation (TFI) was used to obtain the coordinates of nodes and determine the sequence of node numbering in the inner finite region including the canyon. The hybrid method, comprising finite element method and a Lamb series, was applied in conjunction with TFI to study the effects of canyon geometry, incident angle of SH waves (), and dimensionless frequency () on . We detailed the amplification of in the illuminated zone and variations in due to canyon-decay-effect along the canyon surface as well as the decay of resulting from the shield effect in the shadow zone. Interestingly, oblique-effects play an important role in the magnification of along the inclined bottom of canyons, and variations in and dominate the patterns of . 相似文献
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Computation of oceanic vertical stability (Brunt-Väisäläfrequency) with an improved density equation
Wang Dong-Ping 《Earth and Planetary Science Letters》1974,24(1):87-90
Vertical stability of a water column can be computed from the formula: where ρ is density, P is pressure, g is gravity, and c is sound speed.Because Ekman's density equation is not consistent with Wilson's sound speed equation, large errors are introduced by combining these two equations to calculate the vertical stability. However, this difficulty can be overcome with the Wang and Millero density equation derived consistently from Wilson's sound speed equation. In addition to its simplicity, the computation of vertical stability from the above formula using Wilson's sound speed equation and Wand and Millero's density equation can be shown to generally give the most accurate results. 相似文献
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《Physics of the Earth and Planetary Interiors》2005,148(2-4):131-148
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