共查询到20条相似文献，搜索用时 15 毫秒
1.
S. O. Ogunade 《Pure and Applied Geophysics》1982,120(1):136-150
A major problem in electromagnetic induction studies in regions of localized source fields, such as the auroral and equatorial electrojet regions, is the source effect. Using an analytical model, the electromagnetic response of a buried conducting cylinder to sheet current and line current excitations has been studied for the period rangeT=5 s to 24 h. The validity of the numerical results obtained from the analytical model are compared with the numerical results obtained from a finite difference model. The results show that for periods less than 30 min, there is no significant difference in the response of the cylinder to both source fields. However, significant differences are observed at longer periods. It was also observed that the equivalent height at which a uniform sheet current at 100 km above the earth's surface can be approximated by a line current varies as a function of the source period. 相似文献
2.
Dongdong Wang Yongxin Gao Cheng Yao Baozhen Wang Mengqiang Wang 《Geophysical Prospecting》2020,68(6):1958-1979
We investigate the seismoelectric/electroseismic wavefields excited by a point source in an air/seawater/three-layered porous medium configuration containing a hydrocarbon layer. The results show that if an explosive source for excitation is used, receivers at seafloor can record the coseismic electromagnetic fields accompanying the P, S, fluid acoustic waves and the interface responses converted from the acoustic waves at seafloor interface and from the seismic waves at the interfaces beneath the seafloor. Employing a vertical electric dipole source shows that, with the exception of the interface responses converted from electromagnetic waves at seafloor, the interface responses converted from transmitted electromagnetic waves at the interfaces beneath the seafloor can also be identified. Given that the strength of the explosive source is within excitation capability of industry air guns, the generated interface responses from the hydrocarbon layer can be detected by current electromagnetic sensors considering the low ambient noise at the seafloor. Our results demonstrate the feasibility of the seismoelectric method applied to marine hydrocarbon exploration. Electroseismic modelling results suggest that it is not practical to employ this method to prospect marine hydrocarbon layer due to the weak interface response signal, unless a much larger current is injected into seafloor. 相似文献
3.
The response of a horizontal conducting cylinder embedded in a uniform conducting earth is studied using mathematical models of uniform and line current source excitation for the period range 10 to 104 s. The line current source is located at heights ranging from 100–750 km above the surface of the earth. From the calculated results, it is shown that for periods greater than 103 s the ratioE
x
/H
y
at the surface of the earth for localized fields, such as the auroral and equatorial electrojet normally situated at heights of about 100 km, is considerably different from that for a uniform source. The results presented also show that the magneto-telluric method of geophysical prospecting for ore bodies in regions of the electrojet may not be very practicable for periods exceeding 103 s. 相似文献
4.
Wallace H. Campbell 《Pure and Applied Geophysics》1990,134(4):541-557
Two current rings have been observed in the equatorial plane of the earth at times of high geomagnetic activity. An eastward current exists between about 2 and 3.5 earth radii (Re) distant, and a larger, more variable companion current exists between about 4 and 9 Re. These current regions are loaded during geomagnetic substorms. They decay, almost exponentially, after the cessation of the particle influx that attends the solar wind disturbance. This review focuses upon characteristics needed for intelligent use of the ring current as a source for induction probing of the earth's mantle. Considerable difficulties are found with the assumption thatDst is a ring-current index. 相似文献
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6.
In this study, a modification to the chemical mass balance (CMB) receptor model presented in an earlier work was expanded to account for the changes in volatile organic compound (VOC) source fingerprints due to atmospheric reactions of VOCs that take place after being emitted to the atmosphere. The photochemical reactions consume VOCs that participate in, causing changes in the source fingerprints. These changes are of considerable magnitude when the travel durations from the source to the receptor (measurement point) are considered. The current study focuses on expansion of the integrated reaction rates of VOCs with ambient reactive species such as OH ? , O3, NO3, and O ? in order to estimate the source emission profiles simultaneously at the receptor site. Two test cases with different travel times and with different ambient OH ? , O3, and NO3 concentrations were also provided to compare the standard model, the modified model suggested in the previous work, and the current modification. F‐tests were also performed to determine whether the changes in source compositions are significant or not. The results from both the standard model and the modified model were evaluated in terms of χ2, R2, percent mass apportioned (MA), and a best fit (BF) measure. Maximum values of BF for the test cases from the three models were 0.70 ± 0.03, 0.74 ± 0.05, and 1.000 ± 0.00, respectively, indicating that the current modification increases the performance of two previous models and was better in explaining the effects of chemical reactions of VOCs. 相似文献
7.
The sinking of dense water down a steep continental slope is studied using laboratory experiments, theoretical analysis and numerical simulation. The experiments were made in a rotating tank containing a solid cone mounted on the tank floor and originally filled with water of constant density. A bottom gravity current was produced by injecting more dense coloured water at the top of the cone. The dense water plume propagated from the source down the inclined cone wall and formed a bottom front separating the dense and light fluids. The location of the bottom front was measured as a function of time for various experimental parameters. In the majority of runs a stable axisymmetric flow was observed. In certain experiments, the bottom layer became unstable and was broken into a system of frontal waves which propagated down the slope. The fluid dynamics theory was developed for a strongly non-linear gravity current forming a near-bottom density front. The theory takes into account both bottom and interfacial friction as well as deviation of pressure from the hydrostatic formula in the case of noticeable vertical velocities. Analytical and numerical solutions were found for the initial (t < 1/f), intermediate (t 1/f), and main (t 1/f) stages, where f is the Coriolis parameter. The model results show that during the initial stage non-linear inertial oscillations are developed. During the main stage, the gravity current is concentrated in the bottom layer which has a thickness of the order of the Ekman scale. The numerical solutions are close to the same analytical one. Stability analysis shows that the instability threshold depends mainly on the Froude number and does not depend on the Ekman number. The results of laboratory experiments confirm the similarity properties of the bottom front propagation and agree well with the theoretical predictions. 相似文献
8.
Abstract The results of laboratory experiments and numerical model simulations are described in which the motion of a round, negatively-buoyant, turbulent jet discharged horizontally above a slope into a rotating homogeneous fluid has been investigated. For the laboratory study, flow visualisation data are presented to show the complex three-dimensional flow fields generated by the discharge. Analysis of the experimental data indicates that the spatial and temporal developments of the flow field are controlled primarily by the lateral and vertical discharge position of the jet (with respect to the bounding surfaces of the container of width W) and the specific momentum (M 0) and buoyancy (B 0) fluxes driving the jet. The flow is seen to be characterised by the formation of (i) a primary anticyclonic eddy (PCC) close to the source, (ii) an associated secondary cyclonic eddy (SCE) and (iii) a buoyancy-driven bottom boundary current along the right side boundary wall. For the parameter ranges studied, the size L p, s and spatial location x p, s of the PCC and SCE (and the nose velocity u N of the boundary current) are shown to be only weakly-dependent upon the value of the mixed parameter M 0Ω/B 0, where Ω is the background rotation rate. Both L p and x p are shown to scale with the separation distance y?/W of the right side wall (y = 0) from the source (y = y?), both L s and x s scale satisfactorily with the length scale l M (= M 0 3/4/B 0 ½) and u N is determined by the appropriate gravity current speed [(g']0 H]½ and the separation distance y?/W. Numerical model results show good qualitative agreement with the laboratory data with regard to the generation of the PCC, SCE and boundary current as characteristic features of the flow in question. In addition, extension of the numerical model to diagnose potential vorticity and plume thickness distributions for the laboratory cases allow the differences in momentum-and buoyancy-dominated flows to be clearly delineated. Specifically, the characteristic features of the SCE are shown to be strongly dependent upon the value of M 0Ω/B 0 for the buoyant jet flow; not least, the numerical model data are able to confirm the controlling role played by the boundary walls in the laboratory experiments. Quantitative agreement between the numerical and laboratory model data is fair; most significantly, the success of the former model in simulating the dominant flow features from the latter enables the reliable extension of the numerical model to be made to cases of direct oceanic interest. 相似文献
9.
对测氡仪器进行定期校准是保证测量结果准确性和可靠性的关键。基于用国际公认的计量传递仪器AlphaGUARD P2000F作为氡气溯源仪器及其自带水氡测量组件对三套DDL-1型电离法测氡仪使用水中溶解氡进行校准实验。实验结果和用固体氡源校准三套仪器的结果与仪器出厂校准结果进行对比,两种校准方法的K值相对误差均小于5%,达到目前地震监测氡观测技术要求。实验结果表明,水中溶解氡代替固体氡气源校准,可以解决目前固体氡源校准中存在的运输困难、维修技术要求高、国家环保部门监管严格等问题,为地震氡观测仪器校准技术找到了一种新的途径。 相似文献
10.
R.D. Hibbs F.W. Jones V. Ramaswamy H.W. Dosso 《Physics of the Earth and Planetary Interiors》1978,16(4):327-340
This work compares experimental analogue model measurements and finite-difference numerical calculations of the electric and magnetic fields for a highly conducting slab embedded in a poorly conducting host earth for three different source field configurations. Measurements and calculations were carried out for a uniform source, a sheet current source with a y exp(?ay) current intensity distribution, and a horizontal magnetic dipole source. The results indicate reasonable agreement with some exceptions between the analogue and numerical methods. The source field is found to have an important effect on the field anomalies at the interface of the highly conducting slab and the poorly conducting host medium. 相似文献
11.
We propose a mathematical representation to qualitatively describe the spatio-temporal slip evolution during earthquake rupture
in an efficient and easy-to-use manner for numerical simulations of strong ground motion. It is based on three basis functions
and associated expansion coefficients. It is an extension of the approach of Ide and Takeo, (J Geophys Res, 102:27379–27391, 1997). We compare our approach and theirs using simple kinematic source models to illustrate differences
between the two approaches, and show that our approach more accurately represents the spatio-temporal slip evolution. We also
propose a technique based on our representation for extracting a spatio-temporal slip velocity function from a kinematic source
model obtained by the conventional source inversion. We then demonstrate the feasibility of our procedure with application
to an inverted source model of the 26 March 1997 Northwestern Kagoshima, Japan, earthquake (M
W6.1). In the simulations for actual earthquakes, source models obtained from kinematic source inversions are commonly employed.
Our scheme could be used as an interpolation method of slip time functions from relatively coarse finite-source models obtained
by conventional kinematic source inversions. 相似文献
12.
Wen-Yao Xu 《Pure and Applied Geophysics》1989,131(3):371-393
Geomagnetically quiet day variations in the polar region are reviewed with respect to geomagnetic field variation, ionospheric plasma convection, electric field and current. Persistently existing field-aligned currents are the main source of the polar regionSq. Consequently, the morphology and variability of the polar regionSq largely depend upon both field-aligned currents and ionospheric conductivity. Since field-aligned currents are the major linkage between the ionosphere and the magnetosphere, the latter is controlled by solar wind state, in particular, the interplanetary magnetic field, the polar regionSq exhibits remarkable IMF dependence. 相似文献
13.
Ebun Oni 《Pure and Applied Geophysics》1972,101(1):162-173
Summary In low latitude the spatial distribution functions of the source field over the surface and the dimensions of the source, are important in any theory of electromagnetic induction developed for studying the conductivity structure of the Earth. The author has built up a mathematical structure for a theory of electromagnetic induction in anyn-layered earth model in low latitude. No simple solution is assumed for the horizontal distribution function of the source field and no assumption is made about the horizontal gradients of the source. The mathematical structure involves the concept of downward continuity of the field equations inside then-layered earth model. The resulting mathematical functions derived for anyn-layered earth model are complex. Hence a new matrix algebra of complex numbers is introduced by the author and this is built into the theory. From the upward continuity of the field equations, an inequality equation is derived in order to determine the heighth
0 at which the induction field of the earth becomes negligible compared with the source field. The comparison of such heights at two or more stations under the same influence of the source field can be used for the resolution of the lateral distribution of the earch conductivity structure at these stations. The application of the theory will follow in a subsequent paper. 相似文献
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蓝藻水华暴发期间太湖贡湖湾某水厂水源水及出厂水中微囊藻毒素污染分析及健康风险评价 总被引：1，自引：1，他引：0
水体富营养化导致的有害蓝藻水华仍是目前全世界普遍面临的水环境问题,而有害蓝藻水华所引起的饮用水安全问题亦受到人们的广泛关注.为了解太湖水源地水源水及自来水厂出厂饮用水中微囊藻毒素(MCs)的污染现状,于2014年8月期间对贡湖湾某水厂水源水及出厂水中浮游植物胞内及胞外MCs浓度进行了调查,并同时检测了相关的理化指标.结果表明,水源水中胞内MCs总浓度平均值为7165.5 ng/L,以MC-LR和MC-RR为主,平均浓度分别为3408.7和3398.8 ng/L,其中MC-RR占总MCs比例的平均值为56.1%;而胞外溶解性MCs浓度相对较低,平均浓度为142.6 ng/L,最高浓度仅为512.8 ng/L.水厂出厂水中胞内MCs的检出浓度(平均值为0.77 ng/L)和检出频率都很低,去除率达99.8%以上;而胞外溶解性MCs的检出浓度(平均值为21.71 ng/L)和检出频率相对较高,但浓度仍远低于国家标准1.0μg/L,其去除率相对较低,仅为62.9%~81.8%.数据分析发现,水源水中胞内与胞外MCs浓度之间呈显著正相关,胞内MCs浓度与总氮(TN)浓度、铵态氮(NH+4-N)浓度、总磷(TP)浓度、高锰酸盐指数(CODMn)和浊度呈显著相关,而胞外MCs浓度与TN浓度、TP浓度、CODMn、浊度和叶绿素a浓度呈显著正相关;逐步回归结果显示,TP对胞内MCs浓度变化的解释率最高,而胞外MCs浓度变化主要与胞内MCs浓度相关.最终,通过对出厂饮用水中MCs浓度非致癌风险指数的计算发现,出厂饮用水对人类健康的威胁较小,但致癌风险相对较高. 相似文献
17.
Sarva Jit Singh 《Pure and Applied Geophysics》1967,67(1):83-94
Summary The problem of a point source in an isotropic, inhomogeneous fluid medium is discussed. It is assumed that the density of the fluid is constant and the acoustic velocity varies with depth asc=c
0(1 +m z) wherem is a constant andc
0 is, the velocity at the level of the origin. An approximate expression for the field due to a point source in such a medium is obtained when the medium is infinite as well as when it is semi-infinite. It is found that the results obtained agree with the WKB solution of the problem. 相似文献
18.
D. PATELLA 《Geophysical Prospecting》1972,20(3):561-579
In this paper it is shown how one may obtain a generalized Ohm's law which relates the induced polarization electric field to the steady-state current density through the introduction of a fictitious resistivity defined as the product of the chargeability and the resistivity of a given medium. The potential generated by the induced polarization is calculated at any point in a layered earth by the same procedure as used for calculating the potential due to a point source of direct current. On the basis of the definition of the apparent chargeability ma, the expressions of ma for different stratigraphie situations are obtained, provided the IP measurements are carried out on surface with an appropriate AMNB array. These expressions may be used to plot master curves for IP vertical soundings. Finally some field experiments over sedimentary formations and the quantitative interpretation procedure are reported. 相似文献
19.
G.R.J. Cooper 《Geophysical Prospecting》2014,62(5):1169-1179
This paper introduces the conversion of Euler's equation from a Cartesian coordinate system to a radial coordinate system, and then demonstrates that for sources of the type 1/rN (where r is the distance to the source, and N is the structural index) it can be solved at each point in space without the need for inversion, for a known structural index. It is shown that although the distance to the source that is obtained from Euler's equation depends on the structural index used, the direction to the source does not. For some models, such as the gravity and magnetic response of a contact, calculation of the analytic signal amplitude of the data is necessary prior to the application of the method. Effective noise attenuation strategies, such as the use of moving windows of data points, are also discussed. The method is applied to gravity and magnetic data from South Africa, and yields plausible results. 相似文献
20.
J. R. Johler 《Pure and Applied Geophysics》1957,37(1):116-126
Summary The introduction of precision radio navigation systems employing pulse techniques and the ever increasing interest in spherics have stimulated considerable interest in the propagation of the ground wave transient over the surface of the earth. The theory of the propagation of a transient radio frequency ground wave over a finitely conducting plane earth is presented for the particular case of theNorton surface wave by a consideration of a wave, interrupted abruptly at one point in time (t=0), a wave interrupted abruptly at two points in time (t=0,T
2) and a wave interrupted at one point in time followed by an exponential decay. The first case is illustrated by several numerical examples of a cosine current wave applied to a vertical electric dipole source. It is apparent that the method of the inverse aplace transform for the particular cases considered yields some simple mathematical formulas. 相似文献