Non-polarizable Electrodes Research Articles

Electric field variations measured continuously in free air over a conductive thin zone in the tilted Lias-epsilon black shales near Osnabrück, Northwest Germany

Abstract Common studies on the static electric field distribution over a conductivity anomaly use the self-potential method. However, this method is time consuming and requires nonpolarizable electrodes to be placed in the ground. Moreover, the information gained by this method is restricted to the horizontal variations of the electric field. To overcome the limitation in the self-potential technique, we conducted a field experiment using a non conventional technique to assess the static electric field over a conductivity anomaly. We use two metallic potential probes arranged on an insulated boom with a separation of 126 cm. When placed into the electric field of the free air, a surface charge will be induced on each probe trying to equalize with the potential of the surrounding atmosphere. The use of a plasma source at both probes facilitated continuous and quicker measurement of the electric field in the air. The present study shows first experimental measurements with a modified potential probe technique (MPP) along a 600-meter-long transect to demonstrate the general feasibility of this method for studying the static electric field distribution over shallow conductivity anomalies. Field measurements were carried out on a test site on top of the Bramsche Massif near Osnabruck (Northwest Germany) to benefit from a variety of available near surface data over an almost vertical conductivity anomaly. High resolution self-potential data served in a numerical analysis to estimate the expected individual components of the electric field vector. During the experiment we found more anomalies in the vertical and horizontal components of the electric field than self-potential anomalies. These contrasting findings are successfully cross-validated with conventional near surface geophysical methods. Among these methods, we used self-potential, radiomagnetotelluric, electric resistivity tomography and induced polarization data to derive 2D conductivity models of the subsurface in order to infer the geometrical properties and the origin of the conductivity anomaly in the survey area. The presented study demonstrates the feasibility of electric field measurements in free air to detect and study near surface conductivity anomalies. Variations in Ez correlate well with the conductivity distribution obtained from resistivity methods. Compared to the self-potential technique, continuously free air measurements of the electric field are more rapid and of better lateral resolution combined with the unique ability to analyze vertical components of the electric field which are of particular importance to detect lateral conductivity contrasts. Mapping Ez in free air is a good tool to precisely map lateral changes of the electric field distribution in areas where SP generation fails. MPP offers interesting application in other geophysical techniques e.g. in time domain electromagnetics, DC and IP. With this method we were able to reveal a ca. 150 m broad zone of enhanced electric field strength.

Thermodynamic Relation between Voltage-Concentration Dependence and Salt Adsorption in Electrochemical Cells

Electrochemical cells containing two electrodes dipped in an ionic solution are widely used as charge accumulators, either with polarizable (supercapacitor) or nonpolarizable (battery) electrodes. Recent applications include desalination ("capacitive deionization") and energy extraction from salinity differences ("capacitive mixing"). In this Letter, we analyze a general relation between the variation of the electric potential as a function of the concentration and the salt adsorption. This relation comes from the evaluation of the electrical and mechanical energy exchange along a reversible cycle, which involves salt adsorption and release by the electrodes. The obtained relation thus describes a connection between capacitive deionization and capacitive mixing. We check this relation with experimental data already reported in the literature, and moreover by some classical physical models for electrodes, including polarizable and nonpolarizable electrodes. The generality of the relation makes it very useful in the study of the properties of the electric double layer.

Laboratory study of self-potential signals during releasing of CO2 and N2 plumes

Carbon Capture Sequestration (CCS) projects require, for safety reasons, monitoring programmes focused on surveying gas leakage on the surface. Generally, these programmes include detection of chemical tracers that, once on the surface, could be associated with CO2 degassing. We take a different approach by analysing feasibility of applying electrical surface techniques, specifically Self-Potential. A laboratory-scale model, using water-sand, was built for simulating a leakage scenario being monitored with non-polarisable electrodes. Electrical potentials were measured before, during and after gas injection (CO2 and N2) to determine if gas leakage is detectable. Variations of settings were done for assessing how the electrical potentials changed according to size of electrodes, distance from electrodes to the gas source, and type of gas. Results indicated that a degassing event is indeed detectable on electrodes located above injection source. Although the amount of gas could not be quantified from signals, injection timespan and increasing of injection rate were identified. Even though conditions of experiments were highly controlled contrasting to those usually found at field scale, we project that Self-Potential is a promising tool for detecting CO2 leakage if electrodes are properly placed.

Spinal inhibition of descending command to soleus motoneurons is removed prior to dorsiflexion

It has recently been demonstrated that soleus motor-evoked potentials (MEPs) are facilitated prior to the onset of dorsiflexion. The purpose of this study was to examine if this could be explained by removal of spinal inhibition of the descending command to soleus motoneurons. To test this, we investigated how afferent inputs from the tibialis anterior muscle modulate the corticospinal activation of soleus spinal motoneurons at rest, during static contraction and prior to movement. MEPs activated by transcranial magnetic stimulation (TMS) and Hoffmann reflexes (H-reflexes), activated by electrical stimulation of the posterior tibial nerve (PTN), were conditioned by prior stimulation of the common peroneal nerve (CPN) at a variety of conditioning-test (CT) intervals. MEPs in the precontracted soleus muscle were inhibited when the TMS pulse was preceded by CPN stimulation with a CT interval of 35 ms, and they were facilitated for CT intervals of 50-55 ms. A similar inhibition of the soleus H-reflex was not observed. To investigate which descending pathways might be responsible for the afferent-evoked inhibition and facilitation, we examined the effect of CPN stimulation on short-latency facilitation (SLF) and long-latency facilitation (LLF) of the soleus H-reflex induced by a subthreshold TMS pulse at different CT intervals. SLF is known to reflect the excitability of the fastest conducting, corticomotoneuronal cells whereas LLF is believed to be caused by more indirect descending pathways. At CT intervals of 40-45 ms, the LLF was significantly more inhibited compared to the SLF when taking the effect on the H-reflex into account. Finally, we investigated how the CPN-induced inhibition and facilitation of the soleus MEP were modulated prior to dorsiflexion. Whereas the late facilitation (CT interval: 55 ms) was similar prior to dorsiflexion and at rest, no inhibition could be evoked at the earlier latency (CT interval: 35 ms) prior to onset of dorsiflexion. The observation that the CPN-induced inhibition of soleus MEPs disappears prior to onset of dorsiflexion may explain why soleus MEPs are facilitated prior to onset of dorsiflexion contraction. A possible mechanism involves the removal of inhibition of the descending command to the motoneurons at a spinal interneuronal level because the inhibition was seen in LLF and not in SLF, and the MEP inhibition was not observed in the H-reflex. The data illustrate that spinal interneuronal pathways modify descending commands to human spinal motoneurons and influence the size of MEPs elicited by TMS.

Joint Measurement Setup for Determining Spectral Induced Polarization and Soil Hydraulic Properties

The prediction capabilities of unsaturated flow and transport models are often limited by insufficient knowledge about the structural and textural heterogeneity of the soil. To obtain more information about soil structure, texture, and heterogeneity, as well as hydraulic properties, noninvasive spectral induced polarization (SIP) measurements have shown promise. However, there clearly is a need for more detailed investigations on the relation between SIP and hydraulic properties, in particular for unsaturated soil. To address this need, we developed a novel experimental setup that allows simultaneous determination of hydraulic and electrical properties. Our setup consists of multistep outflow equipment for hydraulic measurements and an electrical impedance spectrometer for measurements of the complex electrical conductivity. Two different measurement cells were constructed. The first measurement cell can only be used for nonshrinking soil, while the other one also allows measurements on mildly shrinking soil. Test measurements showed that the measurement accuracy is very high for the complex electrical conductivity. Nonpolarizable point electrodes are used for voltage measurements, ensuring a good contact to the sample for a wide range of water saturations. An experiment performed on unconsolidated sand investigated the dependence of the complex electrical conductivity and fitted Cole–Cole parameters on water saturation. The phase values and chargeability increased with decreasing saturation. The relaxation time associated with a phase peak was independent of saturation and corresponded reasonably to the average grain size of the sand. Therefore, no relationship between relaxation time and unsaturated hydraulic conductivity was found for this well‐sorted sand.

Optimization of organic electrochemical transistors for sensor applications

AbstractDespite the recent interest in organic electrochemical transistors (OECTs) as chemical and biological sensors, little is known about the role that device architecture and materials parameters play in determining sensor performance. We use numerical modeling to establish design rules in two regimes of operation: We find that for operation as an ion‐to‐electron converter, the response of OECTs is maximized through the use of a gate electrode that is much larger than the channel or through the use of a nonpolarizable gate electrode. Improving the conductivity of the polymer and using a channel geometry that maximizes channel width and thickness, and minimizes channel length helps increase the response. For operation as an electrochemical sensor, the sensitivity is maximized in OECTs with gate electrodes that are smaller than their channels. The sensitivity can be improved by increasing the charge carrier mobility and the capacitance per unit area of the conducting polymer, and also its ability to be penetrated by ions from the electrolyte. A channel geometry that maximizes channel width and minimizes channel length also improves sensitivity. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010

Electrochemical behavior of single crystals of nonstoichiometric cerium(III) fluorides

The electrochemical properties of single crystals of cerium fluoride alloyed with bivalent cations Sr2+, Ca2+, Ba2+, Sr2+ + Ca2+, Sr2+ + Ba2+, Ba2+ + Ca2+ and also with La3+ and La3+ + Ba2+ cations are studied using the dynamic voltammetry and impedance spectroscopy. The conductivity of symmetrical cells with Ag electrodes is determined using the method of impedance spectroscopy in the frequency range from 450 to 5 kHz at the temperatures from 20 to 100°C: for CeF3: Sr2+ (0.5 mol %) + Ba2+ (0.5 mol %), σ = σ0 exp[(−0.284 ± 0.005/kT]; for CeF3:Ca2+ (0.5 mol %) + Sr2+ (0.5 mol %), σ = σ0 exp[(−0.292 ± 0.017/kT]. The steady-state and dynamic voltammogams of symmetrical electrochemical cells with nonpolarizable reference electrodes and CeF3 single crystals alloyed with Sr2+, Ca2+, and Ba2+ bivalent cations exhibited ohmic polarization. For cells with CeF3 containing La3+ as an admixture, a hysteresis was observed, which could not be eliminated by chemical and electrochemical treatment of crystals. In the dynamic voltammetric curves of asymmetric cells with nonpolarizable and silver electrode and CeF3 crystals alloyed with Sr2+, Ca2+, and Ba2+, a range of ideal polarizability (from 0 to ∼−2.7 V), and also cerium redox processes and silver fluorination-boundary regeneration were observed. In the dynamic voltammetric curves of asymmetric cells with CeF3 containing La3+ admixture, no range of ideal polarizability was observed; however, the reactions of silver fluorination and reduction of solid-electrolyte cerium were well pronounced at the corresponding potentials.

Galvanostatic investigation of electrochemical processes at the LaF3/M (M: Ag, Bi) interface

The electrochemical processes at the interface between solid fluorine-conducting electrolyte LaF3(Eu2+ 0.8 mol %) and silver or bismuth electrodes in the two-electrode cell with nonpolarizable reference electrode are studied using the galvanostatic method. The anodic galvanostatic transients of LaF3: Eu2+/Ag and LaF3: Eu2+/Bi interfaces are linearized on the log(η − ηmax), vs. t coordinates, i.e. the rate of LaF3|MF n |M electrode formation is limited by slow surface diffusion of metal adions. The initial portions of cathodic galvanostatic transients in the range of solid-electrolyte lanthanum reduction are approximated by the linear dependence of η on log(1 − √t/τ). The plots of logI vs. 1/η are linear both for the lanthanum reduction and for silver and bismuth oxidation involving mobile fluoride ion of solid electrolyte, which is typical for two-dimensional growth of new phase.

Resistivity Measurement of a Small-Volume Sample Using Two Planar Disc Electrodes and a New Geometric Factor

In this work, we derive a new geometric factor in oblate spheroidal coordinates for conductivity or resistivity measurements using two planar disc electrodes based on the electromagnetic field theory and neglecting the electrode polarization effects. The experiments were conducted on saline solutions contained in a grounded metallic bath to validate the obtained values of the derived geometric factor. The effect of the polarization impedance at the electrodes is found to be negligible when using relatively nonpolarizable silver-silver chloride electrodes at a frequency of 3 kHz. Our experimental results also show that the resistivity values determined using both the new geometric factor and a commercial conductivity meter are in good agreement for small electrode radius, interelectrode spacing and depth of sample, therefore making it a promising technique for applications in microfluidics devices. The effects of current density and temperature on the measurement results are also presented.

Impedance analysis of bio-fuel cell electrodes

To determine the criteria for the selection of an electrode suitable for a bio-fuel cell (BFC), five electrodes, i.e. silver, aluminum, nickel, stainless steel and carbon fiber cloth were investigated. The performance of the BFC according to the electrode material, including the generated voltage, current density and power density was observed. These results show that the materials used for constructing the electrodes affect the performance of the BFC. An impedance analysis was used to describe the characteristics of the electrodes in the solution. Equivalent circuits of each component such as solution, electrodes–solution interface and electrode were determined from the impedance data. The constant-phase element (CPE) model was applied for data analyzing. It was found that stainless steel, nickel and aluminum behaved like a polarized electrode which has a high electrode–solution interfacial impedance, while carbon fiber cloth and silver had a low impedance like a non-polarized electrode. The impedance data indicated that a higher interfacial impedance will result in a higher loading effect. The results can be summarized that the carbon fiber cloth electrode offers a good electron transfer in the system and thus supplies higher power to the external load.

Monitoring of an infiltration experiment using the self‐potential method

An infiltration test was performed from a ditch with the purpose of monitoring the evolution of the piezometric levels using self‐potential measurements made at the ground surface. We used a set of 18 piezometers and a network of 41 nonpolarizable (Pb/PbCl2) electrodes. The variations of the self‐potential signals are linearly correlated to the piezometric level changes with an apparent voltage coupling coefficient of −5.5 ± 0.9 mV m−1. We measured, independently of this infiltration test, the three material properties entering the macroscopic field equations. They are the resistivity distribution of the soil, its mean hydraulic conductivity, and its intrinsic streaming potential coupling coefficient (−5.8 ± 1.1 mV m−1). Then, we modeled numerically the infiltration test and the associated self‐potential signals using a two‐dimensional finite difference code. The numerical model reproduces fairly well the observed results. This investigation demonstrates the effectiveness of the self‐potential method in field conditions to monitor small variations (<0.60 m) of the water table. It offers for the first time a test of the electrokinetic theory in the field with independent evaluation of the material properties entering the field equations.

Nature of the potential of nonpolarized zinc electrode in zincate solutions

The effect of components of alkaline zincate solution and surface compounds, which form on metal zinc in the alkaline solutions, on the nature of nonpolarized electrode potential (E) is studied. It is proposed to determine the nature of E by taking into account more rigorously the activities of all solution components. It is found that in the zincate solutions, the potential of nonpolarized metal zinc is the potential of Zn/Zn(OH)2, OH− electrode of the second kind.

AC Electrocorticographic Correlates of Peri-Infarct Depolarizations during Transient Focal Ischemia and Reperfusion

Several studies have highlighted a delayed secondary pathology developing after reperfusion in animals subjected to prolonged cerebral ischemia, and recently we have shown that peri-infarct depolarizations (PIDs) occur not only during ischemia, but also in this delayed period of infarct maturation. Here we study the electrocorticographic (ECoG) manifestations of PIDs as signatures of developing secondary pathology. DC- and traditional AC-ECoG signals were recorded continuously from epidural, nonpolarizable electrodes during 2 h of middle cerebral artery occlusion (MCAo) and 22 h of reperfusion in freely behaving rats. During MCAo, seizures and PIDs recurred frequently and their incidence was significantly correlated. After reperfusion, seizures and PIDs ceased, and for the next several hours delta wave abnormalities dominated the ECoG with progressively increasing amplitude. After a variable period (5 to 15 h), the ECoG amplitude decremented with the onset of a prolonged repetitive series of PIDs. Initial PIDs in this delayed phase produced transient depressions of the high amplitude ECoG signal, but thereafter the ECoG was persistently attenuated, with no transient depressions during subsequent PIDs. The time of onset of postreperfusion PIDs, and hence measures of ECoG attenuation, correlated with 24 h infarct volumes. PIDs could always be detected in baseline shifts of the AC-ECoG signal with a low high-pass cutoff setting. These results suggest that delayed PIDs after reperfusion contribute to a complex secondary pathology involving delayed edema, intracranial hypertension, and hypoperfusion. The manifestation of PIDs in ECoG/electroencephalography recordings may enable continuous real-time monitoring of infarct progression.

Methane oxidation on composite ruthenium electrodes in YSZ cells

The performance of RuO x –ZrO 2 (8 mol%Y 2O 3) composite SOFC electrodes for electrochemical oxidation of methane was evaluated. The main products detected in the temperature range 773–923 K were CO and H 2, with selectivity over 80% and 90%, respectively, i.e., partial oxidation of methane was the dominant electrochemical process. Oscillatory behavior with variation of P CH 4 and current imposition was also observed. Post-run temperature programmed oxidation (TPO) experiments showed the absence of carbon deposition. Current vs. potential measurements revealed that composite RuO x –ZrO 2 (8 mol%Y 2O 3) anodes prepared using combustion synthesis behave as non-polarizable electrodes.

Electrocorticographic evidence of deteriorating penumbral conditions associated with delayed peri-infarct depolarizations following reperfusion in rat focal cerebral ischemia

Changes in electroencephalographic (EEG) activity following focal cerebral ischemia include focal slowing, voltage attenuation, and the waxing and waning of stereotyped activities including PLEDs, seizures, and interictal discharges. However, spreading depolarizations (SD), in the form of cortical spreading depression or peri-infarct depolarizations, are the dominant electrophysiologic events after middle cerebral artery occlusion (MCAo), occurring not only during ischemia but also in a 'secondary phase' throughout the period of infarct maturation 8–24 h post-ischemia. Here we study manifestations of SDs in electrocorticographic (ECoG) patterns to investigate ECoG diagnostics of depolarization events and characterize effects of secondary phase, post-reperfusion depolarizations. Monopolar ECoG signals were recorded continuously from epidural, non-polarizable electrodes during 2 h of MCAo and 22 h reperfusion in freely behaving rats. Recordings were made frontal and parietal electrodes adjacent to the presumed 'penumbra'. Signals were amplified for recording of DC potential and traditional AC-coupled ECoG (0.5–50 Hz band pass). During 2 h MCAo, ECoG amplitude was suppressed relative to baseline. Brief (mean: 72 sec) seizures and SDs (mean: 14 events) recurred frequently but without temporal relationship to each other. During SD, ECoG amplitude remained constant, indicating penumbral conditions (Figure 1, top). Following reperfusion, seizures and SDs ceased, ECoG amplitude recovered, and over the next several hours pathologic delta waves (polymorphic delta activity and PLEDs) dominated the ECoG with progressively increasing amplitude. After a variable period (4–12 h), the ECoG amplitude decreased dramatically in association with the onset of a prolonged repetitive series of depolarizations (mean: 58 events). Initial depolarizations in this phase produced transient depressions of the high amplitude ECoG signal (Figure 1, middle). After several repetitive depolarizations, however, the ECoG became permanently depressed, with no further transient depressions during subsequent depolarizations (Figure 1, bottom). These results were confirmed with bipolar ECoG recordings from penumbral regions. Finally we show that depolarizations could be detected in baseline shifts of the AC-ECoG signal with a low (0.03 Hz) high-pass cutoff setting. Baseline shifts signalled the derivative of the DC potential. The progressive decrement and then permanent depression of the ECoG caused by secondary phase SDs evidences deleterious effects of post-reperfusion depolarizations, and likely the progressive recruitment of penumbral and/or core-infarcted tissue. Furthermore, the lack of transient ECoG depression during SD in this period demonstrates penumbral conditions and suggests that depolarizations can be manifested as 'peri-infarct depolarizations' even following reperfusion.

Characterization of transport properties of argillaceous sediments: Application to the Callovo‐Oxfordian argillite

We consider the case of a cylindrical cored specimen of a saturated argillaceous sediment located between two reservoirs filled with an electrolyte. One of the boundaries of the sample is submitted to a sharp pressure (or salinity change). The migration of the resulting pressure (or saline) front through the core specimen is responsible for the apparition of an electrical field, which is called the streaming potential (the diffusion potential for a salinity gradient, respectively). The temporal variation of this electrical field is recorded with Ag/AgCl nonpolarizable electrodes and used to monitor the evolution of the pressure (or saline) front between the two reservoirs. There is a finite interval of time before which the steady state condition holds through the core. In both cases, the electrical potentials exhibit a relaxation with a relaxation time constant depending on the square of the length of the cylindrical core specimen and on its hydraulic (or ionic) diffusivity. The experiments described here provide new methodologies to determine the hydraulic and ionic diffusivities of clay‐rich materials. These experiments confirm also the predictions of a transport model developed recently for such materials and illustrate a powerful geophysical method to obtain transport properties, not only in the laboratory, but also in the field using a network of nonpolarizable electrodes to remotely monitor dissipation processes occurring inside the investigated system.

Microtubular Hydrogen Electrode, a Reference Electrode for Electrochemical Analyses

This paper describes a new type of miniature hydrogen electrode that is composed of a tubular polymer electrolyte and is suitable for use as the reference electrode in electrochemical measurements. The tubular hydrogen electrode was fabricated by supporting platinum black powder inside a perfluorinated polymer electrolyte tube and feeding hydrogen gas into the tube. It can be used as the reference electrode for electrochemical measurements both in acid electrolyte solutions and in a testing apparatus, for example, in polymer electrolyte fuel cells. The specific feature of the tubular hydrogen electrode is that it is so small that it can fit in microanalytical or electrochemical cell systems. The tubular hydrogen electrode can also work as both a counter electrode and a nonpolarizable reference electrode because of the very large specific surface area of the platinum particles deposited inside. This makes these tubular hydrogen electrodes usable in two-electrode cells, which is another advantage over conventional glass-type hydrogen reference electrodes.

A Sandbox Experiment of Self‐Potential Signals Associated with a Pumping Test

The flow of water in a charged porous material is the source of an electrical field called the streaming potential. The origin of this coupling is associated with the drag of the excess of charge contained in the vicinity of the pore–water interface by the pore fluid flow. In this paper, we present a sandbox experiment to study this “hydroelectric” coupling in the case of a pumping test. A relatively thin Plexiglas tank was filled with homogeneous sand and then infiltrated with tapwater. A pumping test experiment was performed in the middle of the tank with a peristaltic pump. The resulting electrical potential distribution was measured passively at the top of the tank with a network of 27 nonpolarizable electrodes related to a digital multichannel multimeter plus an additional electrode used as a reference. A detectable electrical field was produced at the ground surface and analyzed with analytical solutions of the coupled hydroelectric problem. After the shutdown of the pump, the electrical potential and the piezometric level exhibit similar relaxation times in the vicinity of the pumping well. This means that the electrical potential measured at the ground surface can be used to track the flow of the groundwater and possibly to invert the distribution of the hydraulic transmissivity of the ground.

A Sandbox Experiment of Self-Potential Signals Associated with a Pumping Test

The flow of water in a charged porous material is the source of an electrical field called the streaming potential. The origin of this coupling is associated with the drag of the excess of charge contained in the vicinity of the pore–water interface by the pore fluid flow. In this paper, we present a sandbox experiment to study this “hydroelectric” coupling in the case of a pumping test. A relatively thin Plexiglas tank was filled with homogeneous sand and then infiltrated with tapwater. A pumping test experiment was performed in the middle of the tank with a peristaltic pump. The resulting electrical potential distribution was measured passively at the top of the tank with a network of 27 nonpolarizable electrodes related to a digital multichannel multimeter plus an additional electrode used as a reference. A detectable electrical field was produced at the ground surface and analyzed with analytical solutions of the coupled hydroelectric problem. After the shutdown of the pump, the electrical potential and the piezometric level exhibit similar relaxation times in the vicinity of the pumping well. This means that the electrical potential measured at the ground surface can be used to track the flow of the groundwater and possibly to invert the distribution of the hydraulic transmissivity of the ground.

Self‐potential signals associated with pumping tests experiments

The flow of groundwater during a pumping test experiment is responsible for a measurable electrical field at the ground surface owing to the electrokinetic coupling between the Darcy velocity and the electrical current density. This electrical field can be measured passively with a network of nonpolarizable electrodes connected to a digital multichannel multimeter with a high internal impedance (>10 Mohm). These so‐called self‐potential signals can be used to track the pattern of groundwater flow in the subsurface. A field test was performed using a set of 53 Pb/PbCl2 electrodes plus an additional electrode used as a unique reference in the field and a set of five piezometers to monitor the position of the piezometric surface. Using appropriate Green's functions, the electrical response is analyzed in terms of piezometric head distribution. This new methodology, which we call “electrography,” allows visualization of preferential fluid flow pathways and the distribution of heads during pumping test experiments. Using a conditioning technique, this method could allow inversion of the hydraulic conductivity distribution around a pumping well.