Electric Potential Measurements Research Articles

Experimental study of liquid metal channel flow under the influence of a nonuniform magnetic field

We present an experimental study of a liquid metal flow in a rectangular channel under the influence of an inhomogeneous magnetic field. This is a fundamental problem of liquid metal magnetohydrodynamics that is relevant to the technique of electromagnetic braking in the process of continuous casting of steel as well as for Lorentz force velocimetry. Based on local velocity and electric potential measurements we identify three distinct flow regions; namely (i) a turbulence suppression region, (ii) a vortical region, and (iii) a wall jet region. It is shown that in region (i) the applied inhomogeneous magnetic field brakes the incoming flow in its central part and transforms the velocity profile, which is initially flat, into an M-shaped form. In the central part of the flow, the intensity of the velocity fluctuations is found to decrease strongly. In region (ii) where the magnetic field is strongest, the flow is characterized by large-scale vortical structures which are time dependent for certain values of the control parameters. In region (iii), downstream of the magnetic system, two sidewall boundary layers are observed which generate velocity fluctuations with intensity up to 25% of the mean flow. These boundary layers bear close resemblance to wall jets known from ordinary hydrodynamics. Our experimental data provide a comprehensive database against which numerical simulations and turbulence models can be tested.

Iso-branched semifluorinated alkanes in Langmuir monolayers

A series of semifluorinated n-alkanes (SFAs), of the general formula: (CF 3) 2 CF (CF 2) 6 (CH 2) n H (in short iF9H n), n = 11 – 20 have been synthesized and employed for Langmuir monolayer characterization. Surface pressure and electric surface potential measurements were performed in addition to Brewster angle microscopy results, which enabled both direct visualization of the monolayers structure and estimation of the monolayer thickness at different stages of compression. Our paper was aimed at investigating the influence of the iso-branching of the perfluorinated fragment of the SFA molecule on the surface behavior of these molecules at the air/water interface. It occurred that iF9 SFAs with the number of carbon atoms in the hydrogenated moiety from 11 to 20 are capable of Langmuir monolayer formation. Monolayers from iF9H11 to iF9H13 are instable, whereas those formed by iF9 SFAs with longer hydrogenated chains form stable films at the free surface of water. As compared to SFAs containing perfluorinated chain in a normal arrangement, iso-branched molecules have a greater tendency to aggregate. Lower stability of monolayers formed by iF9 SFAs as compared to F10 SFAs originated from the surface nucleation observed in BAM images, even at the very initial stages of compression. The dipole moment vector for iso-branched SFAs was found to be virtually aligned with the main axis of the molecule, contrary to F10 SFAs, where the dipole moment vector was calculated to be tilted with respect to the main molecular axis. Quantitative Brewster angle microscopy measurements (relative reflectivity experiments) enabled us to monitor the changes of monolayer thickness at different stages of monolayer compression.

Cell Imaging and Manipulation by Nonlinear Optical Microscopy

Advances in the technologies for labeling and imaging biological samples drive a constant progress in our capability of studying structures and their dynamics within cells and tissues. In the last decade, the development of numerous nonlinear optical microscopies has led to a new prospective both in basic research and in the potential development of very powerful noninvasive diagnostic tools. These techniques offer large advantages over conventional linear microscopy with regard to penetration depth, spatial resolution, three-dimensional optical sectioning, and lower photobleaching. Additionally, some of these techniques offer the opportunity for optically probing biological functions directly in living cells, as highlighted, for example, by the application of second harmonic generation to the optical measurement of electrical potential and activity in excitable cells. In parallel with imaging techniques, nonlinear microscopy has been developed into a new area for the selective disruption and manipulation of intracellular structures, providing an extremely useful tool of investigation in cell biology. In this review we present some basic features of nonlinear microscopy with regard both to imaging and manipulation, and show some examples to illustrate the advantages offered by these novel methodologies.

Experimental study of super-rotation in a magnetostrophic spherical Couette flow

We report measurements of electric potentials at the surface of a spherical container of liquid sodium in which a magnetized inner core is differentially rotating. The azimuthal angular velocities inferred from these potentials reveal a strong super-rotation of the liquid sodium in the equatorial region, for small differential rotation. Super-rotation was observed in numerical simulations by Dormy et al. (Dormy, E., Cardin, P. and Jault, D., MHD flow in a slightly differentially rotating spherical shell, with conducting inner core, in a dipolar magnetic field, Earth Planet. Sci. Lett., 1998, 160, 15--30). We find that the latitudinal variation of the electric potentials in our experiments differs markedly from the predictions of a similar numerical model, suggesting that some of the assumptions used in the model – steadiness, equatorial symmetry, and linear treatment for the evolution of both the magnetic and velocity fields – are violated in the experiments. In addition, radial velocity measurements, using ultrasonic Doppler velocimetry, provide evidence of oscillatory motion near the outer sphere at low latitude: it is viewed as the signature of an instability of the super-rotating region.

Fabrication of a microscopic four-point probe and its application to local conductivity measurement

A microscopic four-point probe for local conductivity measurement is presented. The silicon nitride based atomic force microscope (AFM) probe with a V-shaped two-dimensional sliced structure tip is patterned by using a conventional photolithography method. The probe is then etched to four parallel electrodes isolated from each other, for the purpose of performing current input and electrical potential drop measurement. The newly developed four-point AFM probe not only inherits the function of generating AFM surface topography but also has the capability of characterizing the local conductivity simultaneously. The nano-resolution position control mechanism of AFM allows the probe to scan across micrometer sized areas and create a high spatial resolution map of the in-plane conductivities. Experiments have shown this four-point AFM probe to be mechanically flexible and robust. The repeatable conductivity measurements on the surface of aluminum and indium tin oxide (ITO) thin films indicate the technique, which is based on this four-point AFM probe, has potential application for characterizing devices and materials in microscale.

Experimental study on the sensitivity and accuracy of electric potential local flow measurements

A measuring system based on potential difference probes is presented which makes possible the determination of very small values of the velocity in liquid metal flows. The resolution limit, the size of the sensor, and the induction of the static measuring field have always been a compromise. These opposite demands were countered with state of the art analog instrumentation, and by meticulously avoiding potential sources of error such as induced noise and thermoelectricity. The present paper instances the flow driven by a rotating magnetic field, in which the scaling of velocity versus strength of the driving electromagnetic force was examined. Measurements of the transition from a Stokes regime to a laminar boundary layer regime demonstrate the improvement in velocity resolution by about two orders of magnitude.

Microscopic four-point atomic force microscope probe technique for local electrical conductivity measurement

A micro-four-point probe technique for local electrical conductivity measurement is presented. An atomic force microscope (AFM) probe was fabricated into four parallel electrodes isolated from each other. Electrodes separated by a distance as small as 1.0μm were used to perform the current and electrical potential measurements. This technique is a combination of the principles of the four-point probe method and standard AFM. The equipment is capable of simultaneously measuring both surface topography and local electrical conductivity. Experiments show the microprobe to be mechanically flexible and robust. The repeatable conductivity measurement on the submicron surface of thin aluminum and indium tin oxide films demonstrates the capability of the equipment and its possible extension to characterize microdevices and samples.

Study of perfluorooctyl-n-alkanes monolayers at the air–water interface

A series of semifluorinated n-alkanes (SFA), of the general formula: F(CF2)m(CH2)nH, (abbreviated as FmHn) where m=8, and n=6–20 have been synthesized and employed for Langmuir monolayer characterization. Surface pressure and electric surface potential measurements were obtained under a variety of experimental conditions, such as spreading volume, subphase temperature and compression speed. The Langmuir monolayer experiments have been complemented with Brewster angle microscopy results, which enabled both visualization of the film texture and estimation of the monolayer thickness at different stages of compression. Although homologues with short hydrogenated part (F8H8 and F8H10) are not stable at the surface and desorb upon compression, higher homologues (n≥13) are good film-forming materials. The negative sign of the measured surface potential, ΔV, evidences for the orientation of all the investigated molecules, regardless the length of the hydrogenated unit, with their perfluorinated parts exposed towards the air. The analysis of the direction of the molecular dipole moment with respect to the main axis enabled us to estimate that the minimum effective dipole moment is achieved for a molecule oriented at the angle of about 35° to the surface normal. The film thickness, inferred from the relative intensity measurements together with BAM images prove monomolecular structure of SFA spread on the water surface.

A transport model of electrolyte convection through a charged membrane predicts generation of net charge at membrane/electrolyte interfaces

Recent measurements of electrical potentials on cartilage undergoing compression revealed the expected negative streaming potentials due to the presence of fixed negative charge in the cartilage matrix. However, these measurements also detected positive electric potentials extending into the external saline bath. We hypothesized that these positive potentials arise from convective displacement of mobile ions through an extended non-equilibrium double layer at the cartilage/bath interface. To examine this possibility, we developed a model of electrolyte transport across a charged membrane and examined the distribution of electric potential and mobile ion concentrations in response to forced convection. The extended Nernst–Planck and Poisson equations were solved numerically assuming the membrane to be infinitely permeable and infinitely stiff so that neither a streaming potential nor a deformation-induced diffusion potential could occur. First order solutions for forced convection of a mono-monovalent electrolyte through the membrane depicted an altered structure of the extended double layer and the creation of net interfacial electric charge densities with opposing polarity on opposite sides of the membrane. The model predicted an increase of the electric and concentration polarizations with increasing ratio of membrane fixed charge to bath ionic strength, but only up to a point of saturation. In this regime, the non-linear behavior of the equation system reveals modifications of the extended double layers inducing localized electric fields and ion concentration gradients in addition with those induced in the bulk of the membrane. This convection-induced interfacial polarization has not been previously studied in detail and could be an important controlling factor in several situations involving transport and electrokinetic phenomena through charged media.

Statistical Characterization Fabricated Charge-up Damage Sensor

<TEX>$SiO_2$</TEX> via-hole etching with a high aspect ratio is a key process in fabricating ULSI devices; however, accumulated charge during plasma etching can cause etching stop, micro-loading effects, and charge build-up damage. To alleviate this concern, charge-up damage sensor was fabricated for the ultimate goal of real-time monitoring of accumulated charge. As an effort to reach the ultimate goal, fabricated sensor was used for electrical potential measurements of via holes between two poly-Si electrodes and roughly characterized under various plasma conditions using statistical design of experiment (DOE). The successful identification of potential difference under various plasma conditions not only supports the evidence of potential charge-up damage, but also leads the direction of future study.

Use of Linear Polymers To Control the Preparation of Luminescent Organic Microcrystals

Microcrystals of an organic fluorescent dye, 4-octylamino-7-nitrobenz-2-oxa-1,3-diazole, were generated using the reprecipitation method, which is a solvent exchange process. In the presence of polymers, namely, poly(acrylic acid), molecular weight 5100 g mol(-1) and 15 000 g mol(-1), and poly(acrylic acid-co-maleic acid), average molecular weight about 50 000 g mol(-1), used as their sodium salts, the reprecipitation process was strongly accelerated. The reprecipitation kinetics was monitored by UV/vis absorption spectroscopy and revealed a three-step mechanism, each step being influenced by the polymer. The size and shape of the microcrystals were analyzed by fluorescence microscopy. The microcrystals obtained in the presence of polymers were smaller and more regular than those prepared in water alone and were not agglomerated. When the polymer was placed in the reprecipitation medium before introducing the dye solution, the microcrystals displayed a rectangular shape. When the polymer was introduced 20 min after the beginning of the reprecipitation process, intricately structured flowerlike microcrystals were observed. Microanalysis revealed that the microcrystals contained noticeable amounts of polymer. The measurement of the surface electric zeta potential suggested that a proportion of the polymer was present at the microcrystal surface. This work gives a thorough insight into a field where trials have until now been performed in an empirical way. It opens new perspectives to produce low-cost organic microcrystals, potentially useful in optics or pharmaceutical sciences.

Some troubles on the measurement of physiological status in field trees : trans-root electric potential and sap-flow measurement

Some troubles on the measurement of physiological status in field trees : trans-root electric potential and sap-flow measurement

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.

Langmuir Monolayers Characteristic of (Perfluorodecyl)-Alkanes

A series of semifluorinated n-alkanes (SFAs) of the general formula F(CF2)m(CH2)nH, (in short FmHn) where m = 10 and n = 6−20, have been synthesized and employed for Langmuir monolayer characterization. Surface pressure and electric surface potential measurements were obtained under a variety of experimental conditions such as spreading volume, subphase temperature, and compression speed. The Langmuir monolayer experiments have been complemented with Brewster angle microscopy results which enabled both direct visualization of the monolayers structure and estimation of the monolayer thickness at different stages of compression. Our results show that these “nonclassical” film-forming materials, which are completely hydrophobic in nature and do not possess any polar group in their structure, are capable of monolayer formation at the air/water interface. It has been observed that with the increase in the molecule's length, its stability at the free water surface increases. The negative sign of the measured surface potential, ΔV, proves that SFA molecules are oriented at the air/water interface with their perfluorinated parts directed toward the air. The effective dipole moments reach the value of −0.65 ± 0.1 D at the minimum for all stable SFAs. The analysis of the direction of the molecular dipole moment in respect to the main axis enabled us to estimate that the minimum effective dipole moment is achieved for a molecule oriented at the angle of about 35° to the surface normal. The relative intensity measurements allow one to conclude that film molecules are tilted in respect to the surface normal at the vicinity of collapse.

SP AND VES RESPONSES OVER PB-ZN AND ASSOCIATED SULPHIDES MINERALIZED ZONE OF IZZI AREA, NIGERIA

Lead-Zinc mineralization in some parts of Izzi area has attracted a number of private miners into the area. The miners can not be said to have been very successful. This is due to the nature of mineralization which occur in isolated vein-lodes that are fracture controlled. Their information on the mineralization or prospecting has been based on reports of Villagers, Shallow hand-dug pits and of douncing rod exercise. Results of 30 electric Self Potential (SP) measurements at two prospective zones of the locality has positive responses for Sulphide mineralization indicated by high negative SP anomaly along two separate bands. The trend of anomaly shows prospective zones of mineralization in the North-South axis across the area, with dip direction towards the North, following the trend of the shale host rock and along the two prospective bands. Result of seven Vertical Electric Soundings (VES) show that the overburden material to the shale host rock consisting of Sandy-Siltstone and Shaly-Mudstone has average depth between 25-39m, given thickness of 11-19m across the area. The Shale host rock is classified into three layer-zones based on resistivity value. A non mineralized zone, with resistivity value less than 3000 (ohm-m). A mineralized zone with resistivity value between 3000 to 5000 (ohm-m) where sphelarite (Zinc ore) is predominant and a highly mineralized zone with resistivity value between 6000 to 8000 (ohm-m) where Galena (lead ore) is dominant. The two bands are due to faulting . Band A at the down throw portion of the fault corresponds to the topographically low area and Band B at the upthrown, corresponds to high topography zone of the study area. KEY WORDS: Fault-fractures, Vein-lodes, Dip, Contours, Resistivity, Geo-Electric Section, Anomaly and Mineralization Potential. Global Jnl Geological Sciences . Vol.2(1) 2004: 61-66

Transient knockout of photosynthesis mediated by electrical signals.

• In the sensitive species Mimosa pudica electric signals arise when the leaves are stimulated by touching or wounding. Experiments reported here provide information about a photosynthetic response that results from heat-induced electrical signalling in leaves. • Electric potential measurements, combined with chlorophyll fluorescence, as well as gas exchange measurements showed that wounding evokes an electrical signal that travels rapidly into the neighbouring leaf pinna to eliminate the net-CO2 uptake rate. At the same time the PSII quantum yield of electron transport is reduced from c.0.6 to 0.2. Two-dimensional imaging analysis of the chlorophyll fluorescence signal revealed that the yield reduction spreads acropetally through the pinna and via the veins through the leaflets. • To determine the speed of a chemical signal, a part of a pinna was exposed to 14 CO2 . The remaining parts of the leaf were provided with label only when the translocation was extended to 12h, indicating that a chemical signal is much too slow to account for the photosynthetic response after heat stimulation. • The results provide evidence for a role of the electrical signal in the regulation of photosynthesis because the high speed of the signal transduction rules out the involvement of a chemical signal, and the photosynthetic response occurs after the arrival of the electrical signal in the leaf pinna.

Nanoscopic electric potential probing: Influence of probe–sample interface on spatial resolution

Electric potential probing on the nanometer scale elucidates the operation of actively driven conducting, semiconducting, insulating and semi-insulating devices and systems. Spatial resolution of this analysis technique is shown to depend on the time required for the voltage measurement circuit to reach steady state with the local electric potential of the sample. Scanning voltage microscopy on actively biased buried heterostructure lasers reveals this time to be intrinsically long (10−2 s to 1 s) and to depend on material doping type (n- or p-type) and scan direction (to increasing or decreasing sample potential). The bandstructure of the probe–sample interface is examined and is shown to provide high incremental contact resistance to an equivalent circuit model of the measurement circuit. Practical scan speed limits are defined for accurate scanning electric potential measurements given a desired spatial resolution.

Combined Electrical and Magnetic Resistivity Tomography: Synthetic Model Study and Inverse Modeling

Electrical Resistivity Tomography (ERT), which has seen increasingly wide use for environmental monitoring, uses the measurement of electrical potentials induced by a low-frequency electric current source. An alternative technique, magnetometric resistivity (MMR), measures the magnetic fields created by the same type of low-frequency electric current source used for ERT. Combining these two methods and thus the two types of data, provides an opportunity for producing improved subsurface images in a wider range of environments. This paper discusses the use of a fully three-dimensional inverse routine that combines magnetic and electric field measurements. The algorithm is based on a 3-D finite difference forward algorithm. The magnetic fields are modeled by applying the reciprocity theorem to model the electric fields induced by a coil of unit moment at a frequency of one radian per second. Using this method, allows for an adjoint formulation for calculating sensitivities of both magnetic and electric fields with respect to changes in the conductivities of individual cells within the finite-difference mesh. In initial model studies, combined MMR∕ERT surveys were better able to resolve 3-D structures than ERT alone. The paper also considers design issues and choices of arrays for MMR surveys over a simple 3-D model. In this case, an integral-equation modeling algorithm is used to calculate the expected magnetic fields over a simple 3-D model. Several horizontal and buried vertical electric sources with surface magnetic receivers are employed. This work suggests that in-well horizontal arrays produce the strongest anomalous signals, while vertical dipoles provide the best sensitivity to target location.

03/02638 Laboratory measurements of electrical potential in rock during high-temperature water flow and chemical reactions: Bernabé, Y. et al. Geothermics, 2003, 32, (3), 297–310

03/02638 Laboratory measurements of electrical potential in rock during high-temperature water flow and chemical reactions: Bernabé, Y. et al. Geothermics, 2003, 32, (3), 297–310

Nineteenth century Parisian smoke variations inferred from Eiffel Tower atmospheric electrical observations

Atmospheric electrical measurements provide proxy data from which historic smoke pollution levels can be determined. This approach is applied to infer autumnal Parisian smoke levels in the 1890s, based on atmospheric electric potential measurements made at the surface and the summit of the Eiffel Tower (48.7°N, 2.4°E). A theoretical model of the development of the autumn convective boundary layer is used to determine when local pollution effects dominated the Eiffel Tower potential measurements. The diurnal variation of the Eiffel Tower potential showed a single oscillation, but it differs from the standard oceanic air potential gradient (PG) variations during the period 09–17 UT, when the model indicates that the Eiffel Tower summit should be within the boundary layer. Outside these hours, the potential changes closely follow the clean air PG variation: this finding is used to calibrate the Eiffel Tower measurements. The surface smoke pollution concentration found during the morning maximum was 60±30 μg m−3, substantially lower than the values previously inferred for Kew in 1863. A vertical smoke profile was also derived using a combination of the atmospheric electrical data and boundary layer meteorology theory. Midday smoke concentration decreased with height from 60 μg m−3 at the surface to 15 μg m−3 at the top of the Eiffel Tower. The 19th century PG measurements in both polluted and clean Parisian air present a unique resource for European air pollution and atmospheric composition studies, and early evidence of the global atmospheric electrical circuit.