Measuring surface potential components necessary for transmembrane current computation using microfabricated arrays

This study was designed to test the feasibility of using microfabricated electrodes to record surface potentials with sufficiently fine spatial resolution to measure the potential gradients necessary for improved computation of transmembrane current density. To assess that feasibility, we recorded unipolar electrograms from perfused rabbit right ventricular free wall epicardium ( n = 6) using electrode arrays that included 25-μm sensors fabricated onto a flexible substrate with 75-μm interelectrode spacing. Electrode spacing was therefore on the size scale of an individual myocyte. Signal conditioning adjacent to the sensors to control lead noise was achieved by routing traces from the electrodes to the back side of the substrate where buffer amplifiers were located. For comparison, recordings were also made using arrays built from chloridized silver wire electrodes of either 50-μm (fine wire) or 250-μm (coarse wire) diameters. Electrode separations were necessarily wider than with microfabricated arrays. Comparable signal-to-noise ratios (SNRs) of 21.2 ± 2.2, 32.5 ± 4.1, and 22.9 ± 0.7 for electrograms recorded using microfabricated sensors ( n = 78), fine wires ( n = 78), and coarse wires ( n = 78), respectively, were found. High SNRs were maintained in bipolar electrograms assembled using spatial combinations of the unipolar electrograms necessary for the potential gradient measurements and in second-difference electrograms assembled using spatial combinations of the bipolar electrograms necessary for surface Laplacian (SL) measurements. Simulations incorporating a bidomain representation of tissue structure and a two-dimensional network of guinea pig myocytes prescribed following the Luo and Rudy dynamic membrane equations were completed using 12.5-μm spatial resolution to assess contributions of electrode spacing to the potential gradient and SL measurements. In those simulations, increases in electrode separation from 12.5 to 75.0, 237.5, and 875.0 μm, which were separations comparable to the finest available with our microfabricated, fine wire, and coarse wire arrays, led to 10%, 42%, and 81% reductions in maximum potential gradients and 33%, 76%, and 96% reductions in peak-to-peak SLs. Maintenance of comparable SNRs for source electrograms was therefore important because microfabrication provides a highly attractive methods to achieve spatial resolutions necessary for improved computation of transmembrane current density.

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Interpreting high spatial resolution line observations of planet-forming disks with gaps and rings: the case of HD 163296

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038712 ◽

2020 ◽

Vol 642 ◽

pp. A165

Author(s):

Ch. Rab ◽

I. Kamp ◽

C. Dominik ◽

C. Ginski ◽

G. A. Muro-Arena ◽

...

Keyword(s):

Spatial Resolution ◽

High Spatial Resolution ◽

Line Emission ◽

High Angular Resolution ◽

Back Side ◽

Gas Temperature ◽

Disk Model ◽

Gas Density ◽

The Impact ◽

Gas Properties

Context. Spatially resolved continuum observations of planet-forming disks show prominent ring and gap structures in their dust distribution. However, the picture from gas observations is much less clear and constraints on the radial gas density structure (i.e. gas gaps) remain rare and uncertain. Aims. We want to investigate the importance of thermo-chemical processes for the interpretation of high-spatial-resolution gas observations of planet-forming disks and their impact on the derived gas properties. Methods. We applied the radiation thermo-chemical disk code PRODIMO (PROtoplanetary DIsk MOdel) to model the dust and gas disk of HD 163296 self-consistently, using the DSHARP (Disk Substructure at High Angular Resolution) gas and dust observations. With this model we investigated the impact of dust gaps and gas gaps on the observables and the derived gas properties, considering chemistry, and heating and cooling processes. Results. We find distinct peaks in the radial line intensity profiles of the CO line data of HD 163296 at the location of the dust gaps. Our model indicates that those peaks are not only a consequence of a gas temperature increase within the gaps but are mainly caused by the absorption of line emission from the back side of the disk by the dust rings. For two of the three prominent dust gaps in HD 163296, we find that thermo-chemical effects are negligible for deriving density gradients via measurements of the rotation velocity. However, for the gap with the highest dust depletion, the temperature gradient can be dominant and needs to be considered to derive accurate gas density profiles. Conclusions. Self-consistent gas and dust thermo-chemical modelling in combination with high-quality observations of multiple molecules are necessary to accurately derive gas gap depths and shapes. This is crucial to determine the origin of gaps and rings in planet-forming disks and to improve the mass estimates of forming planets if they are the cause of the gap.

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Visualization of Water Distribution in Operating PEMFC Using X-Ray Microscopy

ASME 2009 7th International Conference on Nanochannels, Microchannels and Minichannels ◽

10.1115/icnmm2009-82233 ◽

2009 ◽

Author(s):

Jongrok Kim ◽

Junho Je ◽

Massoud Kaviany ◽

Sang Young Son ◽

MooHwan Kim

Keyword(s):

Electric Current ◽

Spatial Resolution ◽

Current Density ◽

Water Distribution ◽

Active Area ◽

X Ray ◽

Electric Loader ◽

Pohang Accelerator Laboratory

In this investigation, X-ray microscopy (7B2) in Pohang Accelerator Laboratory was employed to visualize the water distribution in operating PEMFC which had 2cm × 2cm active area. This X-ray microscopy has 1μm spatial resolution with 1.5mm × 1.2mm view area. Each image spent about 1.3 second, 0.65 second for exposure and about 0.6 second for data read out. The resistance of the electric loader was changed and electric current and voltage was measured during images were recorded. The water distribution in PEMFC was analyzed with this I-V curve. Water distribution was depend on current density and aggregated on interfaces of layers (GDL, MPL, MEA).

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A New Explanation for the Osmotic Activity and Ionic Composition of Gastric Juice

American Journal of Physiology-Legacy Content ◽

10.1152/ajplegacy.1957.192.1.14 ◽

1957 ◽

Vol 192 (1) ◽

pp. 14-22 ◽

Cited By ~ 1

Author(s):

Warren S. Rehm ◽

Warren H. Dennis ◽

William A. Brodsky

Keyword(s):

Osmotic Pressure ◽

Gastric Juice ◽

Chemical Potential ◽

Ionic Composition ◽

Potential Gradient ◽

Inorganic Ions ◽

Parietal Cells ◽

Inorganic Ion ◽

Potential Gradients ◽

Osmotic Activity

In an attempt to extend a previously proposed theory of gastric HCl production, the possibility is considered that the surface epithelial cells secrete H+ ions and the parietal cells Cl– ions and water. It is postulated that water is transported as a result of its chemical potential gradient between the interstitial fluid and the canalicular lumen of the parietal cells. It is shown that this scheme can quantitatively explain, without further postulates, the high normalities of secretion found in the glycine experiments of Teorell. However, the scheme predicts for pure gastric juice a higher osmotic pressure than that found. Furthermore, the scheme does not offer an explanation for the presence of the other inorganic ions of gastric juice. In an attempt to account for the observed osmotic pressure and the inorganic ion content of gastric juice, the implications are developed of the assumption that the Na+ ions, K+ ions and some of the secreted Cl– ions are transported across the mucosa in the direction of their electrochemical potential gradients. It is shown that the resulting scheme can account for the composition and osmotic pressure of gastric juice at least as well as any of the schemes proposed by other workers. The implications of the present scheme with respect to the problem of the production of hypertonic and hypotonic secretions are discussed.

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Anomalous diurnal variation of atmospheric potential gradient and air‐Earth current density observed at Maitri, Antarctica

Journal of Geophysical Research Atmospheres ◽

10.1002/2016jd025043 ◽

2016 ◽

Vol 121 (21) ◽

pp. 12,593-12,611 ◽

Cited By ~ 3

Author(s):

K. Jeeva ◽

S. Gurubaran ◽

E. R. Williams ◽

A. K. Kamra ◽

A. K. Sinha ◽

...

Keyword(s):

Diurnal Variation ◽

Current Density ◽

Potential Gradient

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Mini Electrodes on Ablation Catheters: Valuable Addition or Redundant Information?—Insights from a Computational Study

Computational and Mathematical Methods in Medicine ◽

10.1155/2017/1686290 ◽

2017 ◽

Vol 2017 ◽

pp. 1-13 ◽

Cited By ~ 3

Author(s):

Stefan Pollnow ◽

Joachim Greiner ◽

Tobias Oesterlein ◽

Eike M. Wülfers ◽

Axel Loewe ◽

...

Keyword(s):

Spatial Resolution ◽

High Spatial Resolution ◽

Computational Study ◽

First Line ◽

Curative Therapy ◽

Spatial Sensitivity ◽

Linear Lesions ◽

Significant Difference ◽

Diagnostic Benefit ◽

Unipolar Electrograms

Radiofrequency ablation has become a first-line approach for curative therapy of many cardiac arrhythmias. Various existing catheter designs provide high spatial resolution to identify the best spot for performing ablation and to assess lesion formation. However, creation of transmural and nonconducting ablation lesions requires usage of catheters with larger electrodes and improved thermal conductivity, leading to reduced spatial sensitivity. As trade-off, an ablation catheter with integrated mini electrodes was introduced. The additional diagnostic benefit of this catheter is still not clear. In order to solve this issue, we implemented a computational setup with different ablation scenarios. Ourin silicoresults show that peak-to-peak amplitudes of unipolar electrograms from mini electrodes are more suitable to differentiate ablated and nonablated tissue compared to electrograms from the distal ablation electrode. However, in orthogonal mapping position, no significant difference was observed between distal electrode and mini electrodes electrograms in the ablation scenarios. In conclusion, catheters with mini electrodes bring about additional benefit to distinguish ablated tissue from nonablated tissue in parallel position with high spatial resolution. It is feasible to detect conduction gaps in linear lesions with this catheter by evaluating electrogram data from mini electrodes.

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Spatial Resolution and Response Compensation of a Fine-Wire Temperature Sensor Used in Turbulence Temperature Fluctuation Measurements

The Proceedings of the Thermal Engineering Conference ◽

10.1299/jsmeted.2020.0150 ◽

2020 ◽

Vol 2020 (0) ◽

pp. 0150

Author(s):

Kohei HABA ◽

Tomoya HOURA ◽

Hirofumi HATTORI ◽

Masato TAGAWA

Keyword(s):

Spatial Resolution ◽

Temperature Sensor ◽

Temperature Fluctuation ◽

Wire Temperature ◽

Fine Wire

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Failure of Flip-Chip Circuit Interconnects under High Current Density

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.118-120.449 ◽

2010 ◽

Vol 118-120 ◽

pp. 449-453

Author(s):

Yu Dong Lu ◽

Xiao Qi He ◽

Yun Fei En ◽

Xin Wang ◽

Zhi Qiang Zhuang

Keyword(s):

Current Density ◽

Flip Chip ◽

Chemical Potential ◽

High Current Density ◽

Potential Gradient ◽

High Current ◽

Wind Force ◽

Chemical Potential Gradient ◽

Solder Bumps ◽

Electron Wind

Both Al interconnects and flip-chip solder bumps were sensitive to high current. The failure mechanism of circuits interconnects would be more complicated if the current density in circuits was exceed the critical magnitudes of electromigration in both Al interconnects and solder bumps. The failure of circuit interconnects under different magnitudes of current density was studied and the interaction of electromigration in solder bumps and Al interconnects was discussed. The circuit interconnects of flip chip show three failure phenomena under high current density: voids in Al final metal, inter-diffusion of Al and SnPb, and melting of solder bumps. The voids in Al metal show the directional diffusion of Al atoms was mainly controlled by the electron wind fore. However the inter-diffusion of Al and SnPb demonstrated the electron wind force to Sn and Pb atoms would be ignored in contrast with chemical potential gradient or intrinsic stress. The flow of Sn and Pb atoms under high current density was in opposite direction with electron wind force and uniform with chemical potential gradient.

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The hydraulic architecture of Thuja occidentalis

Canadian Journal of Botany ◽

10.1139/b83-226 ◽

1983 ◽

Vol 61 (8) ◽

pp. 2105-2111 ◽

Cited By ~ 46

Author(s):

M. T. Tyree ◽

M. E. D. Graham ◽

K. E. Cooper ◽

L. J. Bazos

Keyword(s):

Water Potential ◽

Water Flow Rate ◽

Potential Gradient ◽

Pressure Potential ◽

Thuja Occidentalis ◽

Unit Leaf ◽

Leaf Surface Area ◽

Potential Gradients ◽

Evaporative Flux ◽

Stem Segments

Leaf specific conductivities (LSC's) were measured on stem segments excised from various points within the canopy of eastern white cedar trees, Thuja occidentalis L. LSC is defined as the water flow rate (kilograms per second) through a stem caused by a unit of pressure potential gradient (megapascals per metre) per unit leaf surface area supplied by the stem (square metres). LSC's were measured on stems of various diameters and were found to vary over a factor of 30 in magnitude from 1 × 10−5 kg s−1 m−1 MPa−1 for stems 1 mm in diameter to 3 × 10−4 kg s−1 m−1 MPa−1 for stems 100 mm in diameter. LSC was found to be related to stem diameter (D (millimetres)) by the following empirical formula: LSC = 9.58 × 10−6 × D0.727. LSC's measured on stem segments including a node had significantly lower LSC's than internodal stem segments of the same length. Various water relations parameters were measured on cedar trees on a diurnal basis including evaporative flux, leaf resistance to evaporation, shoot water potential, air temperature, and air humidity. Water potential isotherms were also measured on excised green shoots. From the above data, we estimate that about 15% of the total water evaporated from green shoots comes from stored water while the shoot water potentials are growing progressively negative. The typical peak evaporative flux in midday was 1.5 × 10−5 kg s−1 m−2; using this value and our measured LSC's we estimate that the pressure potential gradients in the stems must be 50 kPa m−1 in stems 100 mm in diameter and 1500 kPa m−1 in stems 1 mm in diameter. Pressure potential gradients were measured in stems 30 to 50 mm in diameter by the pressure bomb technique and were found to be 69 kPa m−1 during a typical afternoon and this confirms the accuracy of the above estimates.

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Vertical electric currents below thunderstorms and showers

Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character ◽

10.1098/rspa.1930.0077 ◽

1930 ◽

Vol 127 (806) ◽

pp. 567-590 ◽

Cited By ~ 47

Keyword(s):

Electric Fields ◽

Potential Gradient ◽

Heavy Rain ◽

Weather Conditions ◽

The Earth ◽

Continuous Record ◽

Long Time ◽

Potential Gradients ◽

Strong Electric Fields ◽

Definite Period

In a previous paper an account has been given of apparatus which was found to be suitable for studying the discharge of electricity from a raised metal point in the strong electric fields which occur at the surface of the ground during thunderstorms and showers. The two methods of observation which were employed consisted, first, in measuring the quantity of electricity of each sign which was discharged from the point in a definite period of time, usually the duration of a storm; and secondly, in obtaining a continuous record of the current from the point throughout a storm. Observations on a number of thunderstorms and showers over a period of several months, by the first method, showed that there was a considerable preponderance of upward discharges of positive electricity, indicating that negative gradients of potential predominated at the surface of the ground in such disturbed weather conditions. Some examples of records obtained by the second method were also given. In the present paper, results obtained by the first method over a period of two years are discussed, the observations including all occasions, during that time, on which intense electric fields existed at the observing station for a sufficiently long time to cause a measurable quantity of electricity to be discharged from the point. (The smallest quantity which would be detected by the integrating device is about 0·1 milli-coulomb.) The preponderance of negative potential gradients during periods of intense electric field has been confirmed over the longer period of time. Records obtained by the second method are also described, and their bearing on the question of the polarity of the clouds is discussed. For this purpose, the method of observation is simply a convenient way of obtaining an unambiguous continuous record of the sign of the potential gradient, and a rough estimate of its magnitude, throughout periods of heavy rain. Finally, the problem of the total interchange of electricity between the earth and the atmosphere from known causes is re-discussed, utilising the results already given.

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