Point Current Source Research Articles

Research on Heavy Oil Thermal Recovery by CO2 Steam Flooding with Help of Combination of Borehole-Surface Electric Potential and Cross-Borehole Electric Potential

With an increasing tendency towards more demand for energy resources, the supply of energy as a focus of global strategy is attracting more and more attention from the world. However, on the one hand, conventional hydrocarbon resources are decreasing gradually, and therefore it is definitely an urgent task to search for renewable and replaceable resources at the present time. On the other hand, it has been proved that the total reserves of heavy oil are already up to 1105×108 tons around the world, which means that exploring heavy oil can be a beneficial supplement for alleviating the shortage of oil and gas. Moreover, it is noteworthy that because the heavy oil can be exploited by heated CO2, collecting and consuming CO2 during the production process will help to relieve global warming. In this study, we take the feasibility of heavy oil recovery by CO2 steam into consideration only from the viewpoint of geophysics. In the process of research, with the help of borehole-surface electric potential and cross-borehole electric potential, the entire procedures from heating heavy oil reservoir and optimizing the location of well to deciding the layer of perforation are exhibited completely. In the course of calculation, potential distributions corresponding to a point source of current are acquired by solving the Poisson equation using a direct and explicit finite difference technique for a lower half-space with 3-D distribution of conductivity. As for computation of a large sparse matrix, the technique of nonzero bandwidth storage and the Incomplete Cholesky Conjugate Gradient method are adopted. The consequences prove that with the assistance of cross-borehole electric potential combining with borehole-surface electric potential, the project of heavy oil recovery by CO2 steam is feasible and effective.

Time-harmonic analysis of grounding system in horizontally stratified multilayer medium

This paper extends an electromagnetic model for time-harmonic analysis of grounding system in horizontally stratified multilayer medium which consists of air and arbitrary number of soil layers. Complete electromagnetic coupling between grounding system segments is taken into account. The model is based on applying the finite element technique to an integral equation formulation. Through an effective approximation of the attenuation and phase shift effects the computation of Sommerfeld integrals has been avoided, which considerably shortens the computational time. The treatment of non-horizontal segments of grounding grid conductors has been resolved by approximating the segment with five current point sources distributed along the segment length. An algorithm for scalar electric potential computation in any soil layers is presented and compared to published results. The effects of approximating a complex heterogeneous earth structure with a homogeneous earth is also analyzed and discussed.

Whales Might Also Be an Important Component in Patagonian Fjord Ecosystems: Comment to Iriarte et al.

Whales Might Also Be an Important Component in Patagonian Fjord Ecosystems: Comment to Iriarte et al.

Modeling deep brain stimulation: point source approximation versus realistic representation of the electrode

Deep brain stimulation (DBS) has emerged as an effective treatment for movement disorders; however, the fundamental mechanisms by which DBS works are not well understood. Computational models of DBS can provide insights into these fundamental mechanisms and typically require two steps: calculation of the electrical potentials generated by DBS and, subsequently, determination of the effects of the extracellular potentials on neurons. The objective of this study was to assess the validity of using a point source electrode to approximate the DBS electrode when calculating the thresholds and spatial distribution of activation of a surrounding population of model neurons in response to monopolar DBS. Extracellular potentials in a homogenous isotropic volume conductor were calculated using either a point current source or a geometrically accurate finite element model of the Medtronic DBS 3389 lead. These extracellular potentials were coupled to populations of model axons, and thresholds and spatial distributions were determined for different electrode geometries and axon orientations. Median threshold differences between DBS and point source electrodes for individual axons varied between −20.5% and 9.5% across all orientations, monopolar polarities and electrode geometries utilizing the DBS 3389 electrode. Differences in the percentage of axons activated at a given amplitude by the point source electrode and the DBS electrode were between −9.0% and 12.6% across all monopolar configurations tested. The differences in activation between the DBS and point source electrodes occurred primarily in regions close to conductor–insulator interfaces and around the insulating tip of the DBS electrode. The robustness of the point source approximation in modeling several special cases—tissue anisotropy, a long active electrode and bipolar stimulation—was also examined. Under the conditions considered, the point source was shown to be a valid approximation for predicting excitation of populations of neurons in response to DBS.

Influence of Power Supply Current in Electrical Landfill Leakage Detection Method

The electrical method is effective on detecting and locating leaks in geomembrane liners for landfills. If a leak exists in the liner, an anomaly in the measured potential is generated in the immediate vicinity of the leak through which electrical current is flowing. But the power supply current above the liner can affect the potential distribution. A current point source model for power supply current was set up in this paper. The potential equation induced by the point source was derived. The analysis of potential expression shows that: 1) the potential generated by the power supply current is proportional to the current size and the medium resistivity; 2) as the medium thickness increases, the potential reduces; 3) to reduce the influence of power supply current, the power supply electrode should be away from the detection area as far as possible.

水平多層構造中の任意電極配置による直流電位応答─点電流源に対する理論電位漸化式の導出─

水平多層構造中の任意電極配置による直流電位応答<br/>─点電流源に対する理論電位漸化式の導出─

Study on the Transmitting Mechanism of CSELF Waves: Response of the Alternating Current Point Source in the Uniform Space

AbstractIn the Controlled Source Extremely Low Frequency (CSELF) method, an antenna composed of very long grounded electrical line is deployed along high resistivity route. Strong currents usually more than one hundred Amps are injected into the earth through the grounding ends, however their flow and distribution characteristics are still not very clear yet. A new idea is put forward in this paper. The antenna is separated into two parts. One part is a long electrical line source with alternating current (AC). The other is an AC point source. The total field can be obtained by the vector sum of the responses excited by both sources. Here the solution to the AC point source in a uniform space is discussed in detail. The responses excited by an AC point source and a DC point source are compared carefully. The results show that there is little difference between an AC point source and a DC point source in the uniform space within a small region (the distance from site to source is about tens or hundreds meters), so an AC point source can be approximated by a DC point source; but in a large region, the attenuation of the field excited by an AC point source is much faster than that of a DC point source. Because the antenna of CSELF is rather long and the distance from site to source is very large in general, thus the distribution of current in the earth satisfies the AC law, and could not be approximated by a DC point source.

Multiple superimposed probability tomography on a second electrical field

Based on the requirement of probability tomography, we developed two-directional pole–pole measurement on a 2D electrical imaging survey which is able to extract all second electrical field profiles to participate in probability tomography. The concept of charge occurrence probability (COP) is defined as the average of cross-correlation of the space domain scanning (SDS) function with the second electrical field being generated by a whole set of point current sources. To quantitatively analyse the results of the tomography, the COP values are normalized. Finally, in order to test the effectiveness of the tomography, we use a finite element algorithm to synthesize the potential data for 2D models, and the profiles of the second electrical field are extracted by eliminating the primary field from the total field. Using the second electrical field of all profiles, the geometric patterns of normalized COP (NCOP) values are reconstructed by means of multiple superimposed probability tomography. The results are quite satisfactory.

The effect of test conditions on the sensitivity and resolution of SRET signal response

PurposeThe aim of this paper is to study and analyse the advantages and limitations of the scanning reference electrode technique (SRET) to detect and assess localised electrochemical activity based on an evaluation of the influence of the principal test parameters on the sensitivity and resolution of the technique.Design/methodology/approachMeasurements of Ohmic potential gradients induced by ionic flux close to a point current source (PCS) were carried out using a scanning reference electrode technique (SRET) instrument, which comprised a vertical rotating working electrode and a scanning probe formed by a pair of platinum electrodes of approximately 200 μm of diameter. Ionic flux was induced by anodic polarisation applied to a gold micro‐disc electrode, which acted as the PCS. Measurements were conducted in electrolytes of ten different conductivities, using different scanning probe tips to sample surface distance and different working electrode rotation rates. The range of conductivities used included most of the possible electrolytes to which metallic materials can be in contact under real service conditions.FindingsThe SRET signal sensed from a polarised PCS showed a strong dependence on the rotation rate of the working electrode for electrolytes of low conductivity but a minimal effect on electrolytes with conductivities higher than 50 mS/cm.Originality/valueThis work presents the effect of wide variations on the electrochemical and operational conditions on the sensitivity and resolution of SRET signal response and discusses the limitations of the technique to assess localised electrochemical activity due to the effect of high conductivity electrolytes, large separation distance between the SRET scanning probe and developing dissolution and scanning rate of a the localised site.

MATHEMATICAL METHODS IN ELECTROMAGNETIC THEORYSourwise Representation of the Field Green's Function of a Circular Waveguide

The singularity part of the electrical Green’s function for a circular waveguide field is singled out in an explicit form as a Green’s function for the infinite space. The problem of the Green’s function construction for a field is solved as a problem of a diffraction of tensor divergent spherical and quasispherical waves on the circular waveguide walls. Spherical and quasispherical waves correspond to the rotational and potential components of the electric field strength of a current point source. Owing to the delay effect, a potential component of the electric field intensity decreases at infinity inversely to the first degree of the distance between the source point and the observation point, unlike the Coulomb field. The analytical expressions for singular and regular parts of the tensor Green’s function and the calculation results of one of its component are given. The effective algorithm of the Green’s function calculation, which can be used for solving the singular and hypersingular integral equations in the problems of microwave techniques, electronics and accelerating techniques is developed.

Potential distribution for a harmonic current point source in horizontally stratified multilayer medium

Purpose – This paper aims to describe a numerical procedure for approximating the potential distribution for a harmonic current point source, which is either buried in horizontally stratified multilayer earth, or positioned in the air. The procedure is very efficient and general. The total number of layers and the source position in relation to the medium model layers are completely arbitrary.Design/methodology/approach – The efficiency of the computation procedure is based on the successful application of the numerical approximation of two kernel functions of the integral expression for the potential distribution within an arbitrarily chosen layer of the medium model. Each kernel function of the observed layer is approximated using a linear combination of 15 real exponential functions. Using these approximations and the analytical integration based on the Weber integral, a simple expression for numerical approximation of potential distribution within boundaries of the observed medium layer is given. Pote...

Construction and Validation of a Plunge Electrode Array for Three-Dimensional Determination of Conductivity in the Heart

The heart's response to electrical shock, electrical propagation in sinus rhythm, and the spatiotemporal dynamics of ventricular fibrillation all depend critically on the electrical anisotropy of cardiac tissue. Analysis of the microstructure of the heart predicts that three unique intracellular electrical conductances can be defined at any point in the ventricular wall; however, to date, there has been no experimental confirmation of this concept. We report the design, fabrication, and validation of a novel plunge electrode array capable of addressing this issue. A new technique involving nylon coating of 24G hypodermic needles is performed to achieve nonconductive electrodes that can be combined to give moderate-density multisite intramural measurement of extracellular potential in the heart. Each needle houses 13 silver wires within a total diameter of 0.7 mm, and the combined electrode array gives 137 sites of recording. The ability of the electrode array to accurately assess conductances is validated by mapping the potential field induced by a point current source within baths of saline of varying concentration. A bidomain model of current injection in the heart is then used to test an approximate relationship between the monodomain conductivities measured by the array, and the full set of bidomain conductivities that describe cardiac tissue.

Asymptotic Fields in Frequency and Time Domains Generated by a Point Source at the Horizontal Interface Between Vertically Uniaxial Media

For a point current source placed at the interface between two half-space media, investigation is made of the far-zone asymptotic fields in the frequency domain and their transient waveforms. The media are electrically uniaxial with the uniaxis normal to the interface. The leading-order fields contributed by the stationary-phase points serve as good approximations well off the critical angles. Near the critical angles, the uniform asymptotic techniques need to be employed for a proper approximation. Unlike the ordinary wave, the extraordinary wave cannot be correctly described merely by taking into account the proximity of the stationary and branch points, except in some rare cases. Consideration must also be given to the combined effect associated with the pole introduced in the formulation. The validities of the asymptotic approximations are examined in the time domain by comparing the asymptotic-field waveforms with the wavenumber-synthetic waveforms, around the critical angle of the extraordinary wave.

Contaminant Exposure of Barn Swallows Nesting on Bayou D'Inde, Calcasieu Estuary, Louisiana, USA

Current and historical point source discharges, storm water runoff, and accidental spills have contaminated the water, sediment, and biota within the Calcasieu Estuary in southwestern Louisiana. In 2003, barn swallow (Hirundo rustica) eggs and nestlings were collected beneath two bridges that cross Bayou d'Inde, the most contaminated waterway within the Calcasieu Estuary. Samples were also collected from a bridge over Bayou Teche, a reference site in south central Louisiana. Polychlorinated biphenyl (PCB) concentrations in barn swallow eggs and nestlings were significantly higher at the downstream site on Bayou d'Inde (2.8 micro g/g PCBs in eggs and 1.5 micro g/g PCBs in nestlings) than at the other two sites (< 0.2 micro g/g PCBs in eggs and nestlings at both sites). Ethoxyresorufin-O-dealkylase activity in nestling livers was significantly higher at the downstream site on Bayou d'Inde (50 pmol/min/mg) compared to the other two locations (24 pmol/min/mg, each), probably because of exposure to PCBs. Polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran concentrations in eggs and polycyclic aromatic hydrocarbons in nestlings were at background concentrations at all sites. Trace element concentrations in barn swallow eggs and nestling livers were at background levels and did not differ among the three sites. A biomarker of DNA damage did not differ among sites.

ANALYTICAL SOLUTIONS FOR NONLINEAR CABLE EQUATIONS WITH CALCIUM DYNAMICS I: DERIVATIONS

The interaction between membrane potential and internal calcium concentration plays many important roles in regulating synaptic integration and neuronal firing. In order to gain a better theoretical understanding between the voltage-calcium interaction, a nonlinear cable equation with calcium dynamics is solved analytically. This general reaction-diffusion system represents a model of a cylindrical dendritic segment in which calcium diffuses internally in the presence of buffers, pumps and exchangers, and where ion channels are sparsely distributed over the membrane,in the form of hotspots, acting as point current sources along the dendritic membrane. In order to proceed, the reaction-diffusion system is recast into a system of coupled nonlinear integral equations, with which a perturbative expansion in dimensionless voltage and calcium concentration are used to find analytical solutions to this general system. The resulting solutions can be used to investigate, the interaction between the membrane potential and underlying calcium dynamics in a natural (non-discretized) setting.

The Total Field Magnetometric Resistivity(TFMMR) Method Part II: 2D resistivity inversion of data from the Flying Doctor Deposit, Broken Hill, Australia

Total field magnetometric resistivity (TFMMR) is a highresolution electrical technique that yields information on subsurface resistivity. In a companion paper (Fathianpour et al., 2005, Part I) the basis of a 2.5D TFMMR finite-element modelling approach was developed for a point current source in an otherwise 2D resistivity structure. In this paper (Part II), we use the 2.5D forward modelling algorithm as the basis of a numerical inversion for 2D resistivity structure using a Marquardt-Levenberg algorithm. Application of a quasi-Newton updating formula for approximating the Fréchet derivatives in the course of inversion results in a fast and reliable routine. To overcome the problems of the effect of the geomagnetic field direction and dependency of TFMMR data on all three vector-components, field data are initially reduced to the pole. By doing this, we require only Fréchet derivatives for the vertical Bz anomalous magnetic field, and in the case of the 2D structures, Bz is the most sensitive component to vertical boundaries separating lateral changes in resistivity.TFMMR data collected across the Flying Doctor Deposit, near Broken Hill in New South Wales, Australia are inverted for 2D resistivity structure. The inverse models show the presence of a conductive zone in the central part of the surveying area corresponding to the known mineralisation and the Globe Vauxhall Shear Zone. Depth resolution is limited, but we demonstrate that the method can resolve lateral boundaries.

Analytical solution of electric potential produced by a direct current point sou rce located in a multilayered spherical volume conductor

A general analytical solution is derived for an electric potential produced by a direct current point source located at any position in a multilayered spher ical volume conductor. Starting from Poisson's equation, the electric potential whose coefficients are rapidly got in the form of matrix expressions is obtained according to the boundary conditions. Simulation for a four-layered spherical volume conductor denoting the scalp, skull, cerebrospinal fluid and brain tissue proves that electric potential in this paper converges more rapidly in the whol e region than that expressed only in spherical harmonics expansion form, and ite rative times decrease. Electric potential contour and current streamline figur es show that it is important to consider the effect of the low conductivity of s kull on electric potential and current flow. The distribution of electric potent ial on the surface of sphere is discussed, which will be useful in electroenceph alography inverse problems, and also in analyzing and interpreting the electric potential measurement.

Numerical Green's Function of a Point Current Source in Horizontal Multilayer Soils by Utilizing the Vector Matrix Pencil Technique

Numerical Green's function approach is proposed to calculate Green's function of a point current source in an arbitrary horizontal multilayer soil. The coefficients of Green's function are straightforwardly sampled in an iterative way in terms of the simultaneous equation system satisfying the pertinent boundary value problem, then the closed-form expression of Green's function for multilayer soil can be given by the vector matrix pencil technology. The approach proposed could be practically applied in grounding problems in an arbitrarily layered soil without needing to derive the analytical expression of Green's function.

A general method for numerical Green's function in arbitrarily layered soils *

Abstract A straightforward approach is developed to calculate Green's function of a point current source in horizontal multi-layer soils. The sampling value of the coefficient of Green's function is obtained in an iterative way in terms of the equation group satisfying the pertinent boundary value problem. Further, the closed-form expression of multilayered soil Green's function can be given by the vector matrix pencil technology. The numerical results are in agreement with those by using other softwares. The approach proposed here is applicable to grounding problems with the structure of arbitrarily layered soil without needing the analytical expression of Green's function.

Experimental validation of electromagnetic edge waves on a PEC wedge

The dyadic Green's function for electric and magnetic fields of a point current source radiating in close vicinity of a perfectly electric conducting wedge (PEC) has been derived through two independent means by Pearson (1986) and by Buyukdura , Goad, and Kouyoumjian (1996). Asymptotically, a so-called the edge wave may be identified when the source and the observation points are in proximity to the edge but widely separated along the edge, and has become part of the canonical problems in asymptotic diffraction theory. Both of the formulations indicated lead to identical asymptotic results. To corroborate the existence of edge waves, a series of measurements has been performed and the measured data are fit to a model based on the asymptotic results. The fit of the data supports the asymptotic form.