On: “Effect of surface polarization on resistivity modeling” by D. Guptasarma (GEOPHYSICS, v. 48, January 1983, p. 98–106).

Geophysics ◽  
1984 ◽  
Vol 49 (3) ◽  
pp. 314-314
Author(s):  
K. Duckworth
Keyword(s):  
Stainless Steel ◽  
Current Density ◽  
Low Frequency ◽  
Input Current ◽  
Steel Cylinder ◽  
Surface Polarization ◽  
Order Of Magnitude ◽  
Current Densities ◽  
A Current ◽  
Effect Of Surface

I am glad to see that this paper confirms the resistive behavior of metallic models when immersed in electrolyte and subject to low‐frequency currents, which my coauthor and I reported in 1978 (Saydam and Duckworth, 1978). It is also gratifying that this paper confirms the transition from resistive to conductive behavior with increase of frequency which we reported in that same paper. However, I must call into question the validity of the conclusions reached by the author of this paper. I do so for several reasons, the first of which is that the author is not entitled to display complex resistivity spectra derived in a model tank environment unless evidence is provided that those spectra are invariant for a range of primary currents extending over at least two decades from an upper limit of 1 mA. I say this because a current of 1 mA, as apparently used by the author, causes severe nonlinearity in tank modeling as my coauthor and I showed in 1978 (Saydam and Duckworth, ibid). In tests of stainless steel which we performed and in tests on pyrite performed by Anderson and Keller (1964) the maximum permissible current density for linear conditions to exist was [Formula: see text]. Current densities at the surface of the aluminum cylinder of 3 cm diameter used by the authors would have been as high as [Formula: see text] when it was located at a depth of 7 mm (as quoted) directly under one of the current electrodes if the delivered current was 1 mA. It seems unlikely that aluminum would behave linearly at current densities 32 times greater than the maximum permissible for either stainless steel or pyrite, but we have no way of knowing because this paper fails to provide any experimental evidence in this regard. However, in the case of the results for a vertical stainless steel cylinder shown by the author in Figure 6 we can readily compute that if a 1 mA input current was used, the current density at the surface of the cylinder closest to the [Formula: see text] electrode would have been [Formula: see text]. Thus, in this case, linearity could only have been ensured by using an input current at least an order of magnitude lower than the 1 mA quoted by the author.

Facet Topography and Dislocation Structure as a Possible Source for Electrical Heterogeneity in [001] TILT Bicrystals of YBa2Cu3O7-δ

1996 ◽  
Vol 54 ◽  
pp. 338-339
Author(s):  
I-Fei Tsu ◽  
D.L. Kaiser ◽  
S.E. Babcock
Keyword(s):  
Grain Boundary ◽  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Electromagnetic Properties ◽  
Length Scale ◽  
Density Values ◽  
Current Densities ◽  
Applied Fields ◽  
A Current

A current theme in the study of the critical current density behavior of YBa2Cu3O7-δ (YBCO) grain boundaries is that their electromagnetic properties are heterogeneous on various length scales ranging from 10s of microns to ˜ 1 Å. Recently, combined electromagnetic and TEM studies on four flux-grown bicrystals have demonstrated a direct correlation between the length scale of the boundaries’ saw-tooth facet configurations and the apparent length scale of the electrical heterogeneity. In that work, enhanced critical current densities are observed at applied fields where the facet period is commensurate with the spacing of the Abrikosov flux vortices which must be pinned if higher critical current density values are recorded. To understand the microstructural origin of the flux pinning, the grain boundary topography and grain boundary dislocation (GBD) network structure of [001] tilt YBCO bicrystals were studied by TEM and HRTEM.

scholarly journals Na channel distribution in vertebrate skeletal muscle.

1986 ◽  
Vol 87 (6) ◽  
pp. 907-932 ◽  
Author(s):  
J H Caldwell ◽  
D T Campbell ◽  
K G Beam
Keyword(s):  
Skeletal Muscle ◽  
Current Density ◽  
Sharp Decrease ◽  
Na Channel ◽  
Na Current ◽  
Na Currents ◽  
Current Densities ◽  
Kinetics Of ◽  
A Current ◽  
Vertebrate Skeletal Muscle

The loose patch voltage clamp has been used to map Na current density along the length of snake and rat skeletal muscle fibers. Na currents have been recorded from (a) endplate membrane exposed by removal of the nerve terminal, (b) membrane near the endplate, (c) extrajunctional membrane far from both the endplate and the tendon, and (d) membrane near the tendon. Na current densities recorded directly on the endplate were extremely high, exceeding 400 mA/cm2 in some patches. The membrane adjacent to the endplate has a current density about fivefold lower than that of the endplate, but about fivefold higher than the membrane 100-200 micron from the endplate. Small local variations in Na current density are recorded in extrajunctional membrane. A sharp decrease in Na current density occurs over the last few hundred micrometers from the tendon. We tested the ability of tetrodotoxin to block Na current in regions close to and far from the endplate and found no evidence for toxin-resistant channels in either region. There was also no obvious difference in the kinetics of Na current in the two regions. On the basis of the Na current densities measured with the loose patch clamp, we conclude that Na channels are abundant in the endplate and near-endplate membrane and are sparse close to the tendon. The current density at the endplate is two to three orders of magnitude higher than at the tendon.

scholarly journals The phase structure and morphology of electrodeposited nickel-cobalt alloy powders

2011 ◽  
Vol 43 (3) ◽  
pp. 313-326 ◽  
Author(s):  
M. Spasojevic ◽  
L. Ribic-Zelenovic ◽  
A. Maricic
Keyword(s):  
Current Density ◽  
Amorphous Powder ◽  
Nanocrystalline Powders ◽  
Content Increase ◽  
Nickel Powders ◽  
Electrodeposited Nickel ◽  
Current Densities ◽  
Two Phases ◽  
A Current ◽  
Deposition Current Density

Cobalt and nickel powders of three different compositions: Ni0.8Co0.2, Ni0.55Co0.45 and Ni0.2Co0.8 were obtained by electrodeposition from an ammonium chloride-sulphate solution. It was shown that the microstructure and morphology of the powders depended on the deposition current density as well as on the bath composition. Amorphous powder of Ni0.8Co0.2 was obtained at the current density higher than 200 mA cm-2, but nanocrystalline powders having the same composition were obtained at current densities lower than 200 mAcm-2. The nanocrystalline powders with lower Ni contents (0.55 and 0.2) obtained at a current density ranging from 40 mA cm-2 to 450 mA cm-2 were solid solutions of two phases, FCC (?-Ni) and HCP (?-Co) ones. The increase of the HCP phase in the powder was a result of both the Co content increase in the powder and decrease of the deposition current density.

Surgical Diathermy

2011 ◽  
Author(s):  
Patrick Magee ◽  
Mark Tooley
Keyword(s):  
Current Density ◽  
The Body ◽  
Heating Power ◽  
Driving Voltage ◽  
Physiological Effects ◽  
Heating Effect ◽  
Surgical Tool ◽  
Average Current ◽  
Current Densities ◽  
A Current

As discussed in Chapter 4, when a voltage is applied across a conductor, a current will flow. If the voltage is applied across the body via suitable electrodes the body becomes part of the circuit and a current will also flow, the magnitude depending on the properties of the tissues in its path, particularly the resistance. This current can cause heating or other physiological effects, depending on the frequency of the driving voltage. The effects of the domestic mains current flowing through the body was discussed in Chapter 6, but different effects occur as the frequency of the voltage is increased. As the frequency goes up, the heating increases but the tissue stimulation decreases and, at frequencies above 100 kHz (i.e. radio frequencies), the effect is entirely heating. This heating effect in the body by electric current is called diathermy, but the location, concentration and how this heat is used is dependant on the electrode design and the current concentration or current density at any point in the circuit. For a certain applied voltage, the average current throughout the circuit will be the same. The current density is the current per unit area, and so if the material in which the current passes is smaller, the heating effect increases. The resistance of the material is proportional to its size, so as the material becomes smaller then its resistance gets larger. The heating power is the product of the current squared and the resistance (power = I2 × R). Surgical diathermy (or electrosurgery) is where either one or both of the electrodes are very small, and it is used to cut and coagulate tissue. The smaller electrode can be made into a pointed surgical tool and localised heating will occur at the tip of the instrument. The smaller and more pointed the instrument is, the greater the current density will be at the tip. This electrode is classified as the active or live one. The current densities around this electrode can be as much as 10 A cm−2, and the total heating power typically around 200 W.

Nonlinear impedance of mineral‐electrolyte interfaces: Part I. Pyrite

Geophysics ◽  
1978 ◽  
Vol 43 (6) ◽  
pp. 1222-1234 ◽  
Author(s):  
J. D. Klein ◽  
R. T. Shuey
Keyword(s):  
Low Frequency ◽  
Reference Electrode ◽  
Nonlinear Behavior ◽  
Hydrogen Gas ◽  
Polarization Curves ◽  
Reaction Products ◽  
Single Interface ◽  
Secondary Reactions ◽  
Current Densities ◽  
A Current

The impedance of the interface between an acidic electrolyte and polished electrodes of pyrite has been investigated at current densities in the nonlinear range (up to [Formula: see text]). The potential across a single interface relative to a reference electrode was measured in response to a current sinusoid of low frequency (0.002 Hz). Polarization curves, or linear plots of current density versus electrode potential, consisted of distorted Lissajous patterns. At peak current densities the interface impedance is low and is dominated by activation controlled reactions involving pyrite dissolution and hydrogen gas evolution. The polarization curves have a series of step‐like features at intermediate potentials due to current‐limited reactions. These secondary reactions involve solid and/or aqueous reaction products from previous reactions. The high impedance portion of each reaction step corresponds to a limit current caused by either depletion of a particular solid reactant or employment of a current larger than can be carried by diffusion of aqueous reactants. Nonlinear behavior of pyrite was found to be independent of carrier type and conductivity. The potential of the anodic pyrite dissolution reaction was weakly dependent on pH. Potentials of cathodic reactions increased with increasing pH, indicating the involvement of [Formula: see text], as demonstrated by the evolution of hydrogen gas and [Formula: see text] gas.

Electromigration Reliability of Electroplated Gold Interconnects

2014 ◽  
Vol 1692 ◽  
Author(s):  
Steve H. Kilgore ◽  
Dieter K. Schroder
Keyword(s):  
Current Density ◽  
Open Circuit ◽  
Constant Current ◽  
Measured Temperature ◽  
Lifetime Distributions ◽  
Current Densities ◽  
Log Normal ◽  
Equipment Application ◽  
A Current

ABSTRACTThe electromigration lifetimes of a very large quantity of passivated electroplated Au interconnects were measured utilizing high-resolution in-situ resistance monitoring equipment. Application of moderate accelerated stress conditions with current density limited to 2 MA/cm2 and oven temperatures in the range of 300°C to 375°C prevented large Joule-heated temperature gradients and electrical overstress failures. A Joule-heated Au film temperature increase of 10°C on average was determined from measured temperature coefficients of resistance (TCRs). A failure criterion of 50% resistance degradation was selected to avoid thermal runaway and catastrophic open circuit failures. All Au lifetime distributions followed log-normal statistics. An activation energy of 0.80 ± 0.05 eV was measured from constant-current electromigration tests at multiple temperatures. A current density exponent of 1.91 ± 0.03 was extracted from multiple current densities at a single constant temperature.

EFFECT OF SURFACE ON CATHODE POLARIZATION DURING THE ELECTRODEPOSITION OF COPPER

1943 ◽  
Vol 21a (4) ◽  
pp. 37-50 ◽  
Author(s):  
W. Gauvin ◽  
C. A. Winkler
Keyword(s):  
Steady State ◽  
Current Density ◽  
Crystal Size ◽  
Cathode Surface ◽  
Surface Condition ◽  
Metal Structure ◽  
Polarization Current ◽  
Cathode Polarization ◽  
Current Densities ◽  
Effect Of Surface

Measurements in a modified Haring cell have shown that at current densities above approximately 0.6 amp. per dm.2, definite values of the cathode polarization are attained during the electrodeposition of copper from acid copper sulphate solutions, providing sufficient time is allowed for the cathode surface to attain a steady state corresponding to the conditions of electrolysis. At lower current densities, the base metal structure is perpetuated in the deposit, and the cathode polarization will depend upon the surface condition of the electrode initially. The results account for the lack of agreement in polarization values obtained by different workers using the Haring cell, and indicate that crystal size is fundamentally related to true current density, rather than to cathode polarization. A method is outlined for obtaining reproducible cathode-polarization–current-density curves, substantially corresponding to steady state values.

Electrically Assisted Compression of Tungsten Carbide and its Implications for Electrically Assisted Machining

2016 ◽  
Author(s):  
Brandt J. Ruszkiewicz ◽  
Laine Mears
Keyword(s):  
Tungsten Carbide ◽  
Current Density ◽  
Cutting Tools ◽  
Compression Tests ◽  
Machining Processes ◽  
Electrically Assisted ◽  
Maximum Current ◽  
Current Densities ◽  
Improve Surface Finish ◽  
A Current

It has been shown that electrically assisted machining has the ability to reduce cutting force, change chip type, and improve surface finish. However, the effect of electricity on tungsten carbide has not been examined, a material often used to create cutting tools used in electrically assisted machining. During machining processes, depending on the type of cut, a small amount of the tool may be in contact with the workpiece. This will lead to an increased current density at that point on the tool which could lead to undesired effects with respect to tool wear and life. This paper conducts electrically assisted compression tests on uncoated tungsten carbide rod to examine the effect of electricity on the material and determine if there are any current densities that cause large magnitude weakening of the tungsten carbide. It is concluded that there is a maximum current density that can be passed through tungsten carbide before thermal softening becomes a problem. At a current density lower than this threshold, electricity has little effect on the strength of the carbide. This work is related to past electrically assisted turning experimentation.

scholarly journals GALVANOTAXIS OF SLIME MOLD

1951 ◽  
Vol 35 (1) ◽  
pp. 1-16 ◽  
Author(s):  
John D. Anderson
Keyword(s):  
Direct Current ◽  
Current Density ◽  
Sodium Citrate ◽  
Sea Water ◽  
Threshold Value ◽  
Lower Threshold ◽  
Current Densities ◽  
Li Ion ◽  
A Current ◽  
Plasmodium Of Physarum Polycephalum

The plasmodium of Physarum polycephalum reacts to direct current by migration toward the cathode. Cathodal migration was obtained upon a variety of substrata such as baked clay, paper, cellophane, and agar with a current density in the substratum of 1.0 µa./mm.2 Injury was produced by current densities of 8.0 to 12.0 µa./mm.2 The negative galvanotactic response was not due to electrode products. Attempts to demonstrate that the response was due to gradients or orientation in the substratum, pH changes in the mold, cataphoresis, electroosmosis, or endosmosis were not successful. The addition of salts (CaCl2, LiCl, NaCl, Na2SO4, NaHCO3, KCl, MgSO4, sodium citrate, and sea water) to agar indicated that change of cations had more effect than anions upon galvanotaxis and that the effect was upon threshold values. K ion (0.01 M KCl) increased the lower threshold value to 8.0 µa./mm.2 and the upper threshold value to 32.0 µa./mm.2, whereas the Li ion (0.01 M LiCl) increased the lower threshold to only 4.0 µa./mm.2 and the upper threshold to only 16.0 µa./mm.2 The passage of electric current produced no increase in the rate of cathodal migration; neither was there a decrease until injurious current densities were reached. With increase of subthreshold current densities there was a progressive decrease in rate of migration toward the anode until complete anodal inhibition occurred. There was orientation at right angles to the electrodes in alternating current (60 cycle) with current density of 4.0 µa./mm.2 and in direct current of 5.0 µa./mm.2 when polarity of current was reversed every minute. It is concluded that the negative galvanotactic response of P. polycephalum is due to inhibition of migration on the anodal side of the plasmodium and that this inhibition results in the limitation of the normal migration of the mold to a cathodal direction. The mechanism of the anodal inhibition has not been elucidated.

In-Situ Scanning Electron Microscope Observations of Strain-Confined Lithium Nucleation at Electrode/Electrolyte Interfaces in All-Solid-State-Lithium Battery

2015 ◽  
Vol 1754 ◽  
pp. 25-30
Author(s):  
Munekazu Motoyama ◽  
Makoto Ejiri ◽  
Yasutoshi Iriyama
Keyword(s):  
Current Density ◽  
High Current Density ◽  
Amorphous Solid ◽  
Number Density ◽  
Cu Film ◽  
Small Cracks ◽  
Current Densities ◽  
A Current ◽  
Scanning Electron

ABSTRACTWe have studied electrochemical Li deposition/dissolution processes at amorphous solid electrolyte (LiPON) interfaces with 30-nm-thick-Cu-current collectors at different current densities by in-situ scanning electron microscopy (SEM). When the current density is smaller than 300 μA cm−2, Li islands continue to grow under a Cu film without coalescing with their neighbors. Consequently, they produce small cracks in the Cu film leading to isolated Li rod growth from the cracks. On the other hand, a current density of 1.0 mA cm−2 provokes the nucleation of Li islands with a higher number density. They rapidly coalesce under a Cu film in all lateral directions before cracking the Cu film. High current density conditions therefore suppress Li rod growths.

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