The simulation of finite ERT electrodes using the complete electrode model

Geophysics ◽  
2011 ◽  
Vol 76 (4) ◽  
pp. F227-F238 ◽  
Author(s):  
Carsten Rücker ◽  
Thomas Günther
Keyword(s):  
Point Source ◽  
Electrode Surface ◽  
Current Source ◽  
Electrical Potential ◽  
Ideal Point ◽  
Point Sources ◽  
Contact Impedance ◽  
Electrode Effect ◽  
Spacing Ratio ◽  
Complete Electrode Model

Direct-current resistivity surveys usually are performed using steel rods of finite extent and grounding resistance. However, in modeling, electrodes are commonly treated as ideal point sources. We present an approach for numerical computation applying the complete electrode model (CEM), which is known from medical imaging. The electrode surface was discretized, and the partial-differential equations were extended by additional relations incorporating a contact impedance and a condition for the current flow through the electrode surface. We verified the modeling of the electrical potential using an analytical solution for a perfectly coupled half-ellipsoid current source. To quantify the influence of a finite electrode, we computed the electrode effect as the ratio between CEM and point-source solution and investigated its dependence on geometry and contact impedance. Surface measurements using rods of typical spatial extent showed electrode effects on the order of the measuring accuracy for an electrode length/spacing ratio lower than 0.2. However, the effects are more significant for closed geometries such as experimental tanks. A comparison with a point approximation for finite electrodes using point-source locations along the electrode axis showed the best agreement, with points at about 60% of the electrode extension. The contact impedance played a minor role for four-point measurements, contributing only a few percent to the electrode effect. In addition to penetrating electrodes, we investigated surface electrodes with galvanic or capacitive coupling, showing electrode effects on the same order as for penetrating electrodes. An inhomogeneous resistivity distribution clearly increased the size of the effects. We also investigate the use of CEM to simulate current injected through steel-cased boreholes. Finally, we applied the approach with buried ring electrodes to calculate effects caused mainly by geometric disturbances from the borehole.

JUSTIFICATION OF POINT ELECTRODE MODELS IN ELECTRICAL IMPEDANCE TOMOGRAPHY

2011 ◽  
Vol 21 (06) ◽  
pp. 1395-1413 ◽  
Author(s):  
MARTIN HANKE ◽  
BASTIAN HARRACH ◽  
NUUTTI HYVÖNEN
Keyword(s):  
Electrical Impedance Tomography ◽  
Electrical Impedance ◽  
Analogous Result ◽  
Real Life ◽  
Point Sources ◽  
Reconstruction Problem ◽  
Contact Impedance ◽  
Impedance Tomography ◽  
Point Electrode ◽  
Complete Electrode Model

The most accurate model for real-life electrical impedance tomography is the complete electrode model, which takes into account electrode shapes and (usually unknown) contact impedances at electrode-object interfaces. When the electrodes are small, however, it is tempting to formally replace them by point sources. This simplifies the model considerably and completely eliminates the effect of contact impedance. In this work we rigorously justify such a point electrode model for the important case of having difference measurements ("relative data") as data for the reconstruction problem. We do this by deriving the asymptotic limit of the complete model for vanishing electrode size. This is supplemented by an analogous result for the case that the distance between two adjacent electrodes also tends to zero, thus providing a physical interpretation and justification of the so-called backscattering data introduced by two of the authors.

Analysis of the Influence of Spot Diameter of Point Sources on HPGE Detector Γ-Ray Efficiencies Simulation for Volume Source

2013 ◽  
Author(s):  
Zining Tian ◽  
Xiaoping Ouyang ◽  
Ming Zeng ◽  
Zhiwei Cheng
Keyword(s):  
Experimental Data ◽  
Monte Carlo ◽  
Point Source ◽  
Hpge Detector ◽  
Ideal Point ◽  
Simulation Method ◽  
Point Sources ◽  
Experimental Simulation ◽  
Small Disk ◽  
Spot Diameter

The concept of transforming the detector efficiency of ϕ 75mm×20mm 13737Cs gas sample to a virtual 137Cs point source simulation, in order to facilitate efficiency evaluations for different source location, was proposed for the HPGe detector. The virtual point source usually has spot diameter, so, analysis of the influence of spot diameter of point source was studied in the present work. It was found that the point source model does not seem to fit too well to the experimental data, for the small source-to-detector distances. A multi-parameter polynomial expression describing the dependence of the count rate versus the source-to detector distance was fitted to the experimental data. The point source (ϕ 4.0mm) and small disk source (ϕ 20mm) were used in this experimental simulation, and their result discrepancy was 5.6%. Monte Carlo simulations were also used to study above experiment process, the discrepancy was 2.6%. For another simulation, the point source (ϕ 4.0mm) and ideal point source (ϕ 0.0mm) were used in Monte Carlo simulation, and their result discrepancy was zero. So, for the whole gas sample simulation, the influence of spot diameter of point source can be neglected in this simulation method.

Sources of Nitrogen and Phosphorus in the Catchment Area of Neusiedlersee/Fertö, Austria/Hungary

1993 ◽  
Vol 28 (3-5) ◽  
pp. 101-110 ◽  
Author(s):  
W. v. d. Emde ◽  
H. Fleckseder ◽  
N. Matsché ◽  
F. Plahl-Wabnegg ◽  
G. Spatzierer ◽  
...  
Keyword(s):  
Point Source ◽  
Catchment Area ◽  
Management Practice ◽  
Water Erosion ◽  
Nonpoint Source ◽  
Point Sources ◽  
Source Control ◽  
Nitrogen And Phosphorus ◽  
Catchment Areas ◽  
The One

Neusiedlersee (in German) / Fertö tó (in Hungarian) is a shallow lake at the Austro-Hungarian border. In the late 1970s, the question arose what to do in order to protect the lake against eutrophication. A preliminary report established the need for point-source control as well as gave first estimates for non-point source inputs. The proposed point-source control was quickly implemented, non-point sources were - among other topics - studied in detail in the period 1982 - 1986. The preliminary work had shown, based on integrated sampling and data from literature, that the aeolic input outweighed the one via water erosion (work was for totP only). In contrast to this, the 1982 - 1986 study showed that (a) water erosion by far dominates over aeolic inputs and (b) the size of nonpoint-source inputs was assessed for the largest catchment area in pronounced detail, whereas additional estimates were undertaken for smaller additional catchment areas. The methods as well as the results are presented in the following. The paper concludes with some remarks on the present management practice of nonpoint-source inputs.

Water quality modeling in the watershed-based approach for waste load allocations

1998 ◽  
Vol 38 (10) ◽  
pp. 165-172 ◽  
Author(s):  
Ruochuan Gu ◽  
Mei Dong
Keyword(s):  
Water Quality ◽  
Point Source ◽  
Water Quality Modeling ◽  
Point Sources ◽  
Low Flow ◽  
Quality Analysis ◽  
Management Approach ◽  
Water Quality Control ◽  
Quality Modeling ◽  
Waste Load

The conventional method for waste load allocations (WLA) employs spatial-differentiation, considering individual point sources, and temporal-integration, using a constant flow, typically 7Q10 low flow. This paper presents a watershed-based seasonal management approach, in which non-point source as well as point sources are incorporated, seasonal design flows are used for water quality analysis, and WLA are performend in a watershed scale. The strategy for surface water quality modeling in the watershed-based approach is described. The concept of seasonal discharge management is discussed and suggested for the watershed-based approach. A case study using the method for the Des Moines River, Iowa, USA is conducted. Modeling considerations and procedure are presented. The significance of non-point source pollutant load and its impact on water quality of the river is evaluated by analyzing field data. A water quality model is selected and validated against field measurements. The model is applied to projections of future water quality situations under different watershed management and water quality control scenarios with respect to river flow and pollutant loading rate.

scholarly journals Presence of Pathogens and Indicator Microbes at a Non-Point Source Subtropical Recreational Marine Beach

2009 ◽  
Vol 76 (3) ◽  
pp. 724-732 ◽  
Author(s):  
Amir M. Abdelzaher ◽  
Mary E. Wright ◽  
Cristina Ortega ◽  
Helena M. Solo-Gabriele ◽  
Gary Miller ◽  
...  
Keyword(s):  
Point Source ◽  
High Tide ◽  
South Florida ◽  
Point Sources ◽  
Fecal Coliforms ◽  
Health Concern ◽  
Ocean Water ◽  
Solar Insolation ◽  
Sources Of Pollution ◽  
Water Detection

ABSTRACT Swimming in ocean water, including ocean water at beaches not impacted by known point sources of pollution, is an increasing health concern. This study was an initial evaluation of the presence of indicator microbes and pathogens and the association among the indicator microbes, pathogens, and environmental conditions at a subtropical, recreational marine beach in south Florida impacted by non-point sources of pollution. Twelve water and eight sand samples were collected during four sampling events at high or low tide under elevated or reduced solar insolation conditions. The analyses performed included analyses of fecal indicator bacteria (FIB) (fecal coliforms, Escherichia coli, enterococci, and Clostridium perfringens), human-associated microbial source tracking (MST) markers (human polyomaviruses [HPyVs] and Enterococcus faecium esp gene), and pathogens (Vibrio vulnificus, Staphylococcus aureus, enterovirus, norovirus, hepatitis A virus, Cryptosporidium spp., and Giardia spp.). The enterococcus concentrations in water and sand determined by quantitative PCR were greater than the concentrations determined by membrane filtration measurement. The FIB concentrations in water were below the recreational water quality standards for three of the four sampling events, when pathogens and MST markers were also generally undetectable. The FIB levels exceeded regulatory guidelines during one event, and this was accompanied by detection of HPyVs and pathogens, including detection of the autochthonous bacterium V. vulnificus in sand and water, detection of the allochthonous protozoans Giardia spp. in water, and detection of Cryptosporidium spp. in sand samples. The elevated microbial levels were detected at high tide and under low-solar-insolation conditions. Additional sampling should be conducted to further explore the relationships between tidal and solar insolation conditions and between indicator microbes and pathogens in subtropical recreational marine waters impacted by non-point source pollution.

scholarly journals On the point-source approximation of earthquake dynamics

2014 ◽  
Vol 57 (3) ◽  
Author(s):  
Andrea Bizzarri
Keyword(s):  
Point Source ◽  
Seismic Waves ◽  
Single Point ◽  
Seismic Source ◽  
Transition Process ◽  
Point Sources ◽  
Multiple Point ◽  
Earthquake Dynamics ◽  
Planar Fault ◽  
Source Models

<p>The focus on the present study is on the point-source approximation of a seismic source. First, we compare the synthetic motions on the free surface resulting from different analytical evolutions of the seismic source (the Gabor signal (G), the Bouchon ramp (B), the Cotton and Campillo ramp (CC), the Yoffe function (Y) and the Liu and Archuleta function (LA)). Our numerical experiments indicate that the CC and the Y functions produce synthetics with larger oscillations and correspondingly they have a higher frequency content. Moreover, the CC and the Y functions tend to produce higher peaks in the ground velocity (roughly of a factor of two). We have also found that the falloff at high frequencies is quite different: it roughly follows ω<span><sup>−2</sup></span> in the case of G and LA functions, it decays more faster than ω<span><sup>−2</sup></span> for the B function, while it is slow than ω<span><sup>−1</sup></span> for both the CC and the Y solutions. Then we perform a comparison of seismic waves resulting from 3-D extended ruptures (both supershear and subshear) obeying to different governing laws against those from a single point-source having the same features. It is shown that the point-source models tend to overestimate the ground motions and that they completely miss the Mach fronts emerging from the supershear transition process. When we compare the extended fault solutions against a multiple point-sources model the agreement becomes more significant, although relevant discrepancies still persist. Our results confirm that, and more importantly quantify how, the point-source approximation is unable to adequately describe the radiation emitted during a real world earthquake, even in the most idealized case of planar fault with homogeneous properties and embedded in a homogeneous, perfectly elastic medium.</p>

scholarly journals Part 2: Odor-Cued Grab Sampling of Transient Environmental Odor Events; Mapping the 'Rolling Unmasking Effect' of Downwind Odor Dispersion

2020 ◽  
Author(s):  
Donald Wright ◽  
Jacek Koziel ◽  
David Parker ◽  
Anna Iwasinska
Keyword(s):  
Point Source ◽  
Sampling Strategy ◽  
Receptor Site ◽  
Final Analysis ◽  
Field Trials ◽  
Point Sources ◽  
Grab Sampling ◽  
Transient Event ◽  
Animal Feeding Operation ◽  
Straight Line

Downwind odor characteristics can be very different depending upon the size of the upwind point-source, interim topography, and wind conditions. At one extreme, the downwind odor plume from a relatively large, confined animal feeding operation (CAFO), located on a flat open plain and under stable, near-straight-line wind conditions can be rather broad, sustained and predictable relative to a fixed receptor site downwind. In contrast, the plume from a small point-source (e.g., a roof vent stack) located on irregular topography and under rapidly shifting wind conditions can be intermittent and fleeting. These transient odor events can be surprisingly intense and offensive, in spite of their fleeting occurrence and perception. This work reports on efforts to optimize an environmental odor sampling strategy, which is optimized for the challenges of (1) sampling of such transient odor 'spikes' and (2) the prioritization of odors/odorants from multiple, closely co-located point-sources, under such transient event conditions. Protocol refinement has emerged by way of 2 environmental odor assessment projects which have been undertaken on behalf of the Missouri Department of Natural Resources. The challenge of transient odor events has been mitigated utilizing rapid, odor cued whole-air grab capture sampling into metalized-FEP gas sampling bags, followed by immediate adsorption transfer onto SPME fibers or sorbent tubes for stabilization during the shipment and storage interval between collection and final analysis. Initial results demonstrated approximately 11 fold increases in target odorant yields for 900 mL sorbent tube transfers from 2-3 second 'burst' odor event bag-captures, as compared to equivalent direct collections at the same downwind receptor location but during perceived (stable) odor 'lull' periods. Results-to-date targeting refinement and field trials of this integrated environmental odor assessment strategy are presented. Preliminary application targeting general odor sampling and point-source differentiation utilizing tracer gases is also presented.

Axisymmetric outflows from binary point-source systems in the presence of an interface

2016 ◽  
Vol 790 ◽  
pp. 205-236
Author(s):  
Lawrence K. Forbes
Keyword(s):  
Binary System ◽  
Point Source ◽  
Numerical Solutions ◽  
Flow Problem ◽  
Surrounding Medium ◽  
Small Deformation ◽  
Point Sources ◽  
Fluid Mixing ◽  
Two Fluids ◽  
Narrow Region

Fluid outflow is considered, from a binary system of two point sources. The sources inject fluid of a lower density than the surrounding medium, and there is a sharp interface separating the two fluids. The overall geometry is taken to be axisymmetric around the line joining the two sources. Numerical solutions are presented for the shape of the interface in unsteady flow, and compared with a linearized solution based on small deformation of the interface from its initial spherical configuration. In addition, a novel spectral method is developed for the solution of the Boussinesq viscous flow problem, accounting exactly for the presence of the two sources and modelling the interface as a narrow region in which fluid mixing is possible. Bipolar outflow jets are seen to be possible.

scholarly journals In situ measurements of speciated atmospheric mercury and the identification of source regions in the Mexico City Metropolitan Area

2009 ◽  
Vol 9 (1) ◽  
pp. 207-220 ◽  
Author(s):  
A. P. Rutter ◽  
D. C. Snyder ◽  
E. A. Stone ◽  
J. J. Schauer ◽  
R. Gonzalez-Abraham ◽  
...  
Keyword(s):  
Point Source ◽  
Mexico City ◽  
Metropolitan Area ◽  
Atmospheric Mercury ◽  
Point Sources ◽  
Rural Site ◽  
Urban Site ◽  
Trajectory Data ◽  
Source Regions ◽  
Rural Sites

Abstract. In order to expand the currently limited understanding of atmospheric mercury source-receptor relationships in the Mexico City Metropolitan Area, real time measurements of atmospheric mercury were made at a downtown urban site, and a rural site on the outskirts of Mexico City, during March 2006. Numerous short-lived increases in particulate mercury (PHg) and reactive gaseous mercury (RGM) concentrations were observed at the urban site during the 17 day study, and less frequent increases in gaseous elemental mercury (GEM) concentrations were measured at both the urban and rural sites. The episodic increases observed were attributed to plume impacts from industrial point source emissions in and around Mexico City. Average concentrations and standard deviations measured during the study were as follows: i) urban site; PHg=187±300 pg m−3, RGM=62±64 pg m−3, GEM=7.2±4.8 ng m−3, and; ii) rural site; GEM=5.0±2.8 ng m−3. Several source regions of atmospheric mercury to the urban and rural sites were determined using Concentration Field Analysis, in which atmospheric mercury measurements were combined with back trajectory data to determine source regions. Only some source regions correlated to mercury emission sources listed in the Federal Pollutant Release and Transfer Register, leaving the rest unaccounted for. Contributions of anthropogenic mercury point sources in and around Mexico City to concentration averages measured at the urban site during the study were estimated to be: 93±3% of reactive mercury (PHg and RGM), and; 81±0.4% of GEM. Point source contributions to GEM measured at the rural site were 72±1%. GEM and reactive mercury (PHg+RGM) were not found to correlate with biomass burning at either of the measurement sites.

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