On: “Depth of Investigation in Direct Current Methods,” by A. Roy and A. Apparao (GEOPHYSICS, October 1971, p. 943–959)

Geophysics ◽  
1972 ◽  
Vol 37 (4) ◽  
pp. 703-704 ◽  
Author(s):  
O. Koefoed
Keyword(s):  
Direct Current ◽  
Electrical Current ◽  
Potential Difference ◽  
Interesting Paper ◽  
Depth Of Investigation

In this very interesting paper, the authors ascribe the potential difference that is measured in resistivity methods to electrical‐current polarization of the subsurface. This description enables them to compare the relative contributions of different portions of the subsurface to the measured potential difference.

Finite Element Analysis for the Evaluation of Cracks at a Pipe-Flange Welded Part by the Direct-Current Potential Difference Method

2015 ◽  
Author(s):  
Naoya Tada ◽  
Masaki Kosaka
Keyword(s):  
Finite Element ◽  
Direct Current ◽  
Difference Method ◽  
Evaluation Method ◽  
Fatigue Cracking ◽  
Potential Difference ◽  
Piping System ◽  
Element Analysis ◽  
Non Destructive ◽  
Current Potential

The use of a flange joint is a popular method to close the end of pipes or connect pipes in manufacturing industries. As the pipes are often subjected to vibrations and cyclic bending, fatigue cracking may occur at the welded part between the pipe and flange. It is therefore important to detect and monitor the cracking in this part to ensure safety of the whole piping system. The direct-current potential difference method (DC-PDM) is known as a suitable non-destructive technique to monitor the initiation and growth of cracks and it has been applied to cracks and wall thinning on the inner surface of pipes. In this study, finite element analyses were carried out to clarify the relationship between the size and location of cracks at the pipe-flange welded part and the potential difference. An evaluation method of circumferential crack length angle by DC-PDM was proposed.

scholarly journals Contribution of axonal orientation to pathway-dependent modulation of excitatory transmission by direct current stimulation in isolated rat hippocampus

2012 ◽  
Vol 107 (7) ◽  
pp. 1881-1889 ◽  
Author(s):  
Anatoli Y. Kabakov ◽  
Paul A. Muller ◽  
Alvaro Pascual-Leone ◽  
Frances E. Jensen ◽  
Alexander Rotenberg
Keyword(s):  
Direct Current ◽  
Cortical Excitability ◽  
Mossy Fiber ◽  
Region Of Interest ◽  
Electrical Current ◽  
Signal Propagation ◽  
Field Vector ◽  
Cortical Region ◽  
Direct Current Stimulation

Transcranial direct current stimulation (tDCS) is a method for modulating cortical excitability by weak constant electrical current that is applied through scalp electrodes. Although often described in terms of anodal or cathodal stimulation, depending on which scalp electrode pole is proximal to the cortical region of interest, it is the orientation of neuronal structures relative to the direct current (DC) vector that determines the effect of tDCS. To investigate the contribution of neural pathway orientation, we studied DCS-mediated neuromodulation in an in vitro rat hippocampal slice preparation. We examined the contribution of dendritic orientation to the direct current stimulation (DCS) neuromodulatory effect by recording field excitatory postsynaptic potentials (fEPSPs) in apical and basal dendrites of CA1 neurons within a constant DC field. In addition, we assessed the contribution of axonal orientation by recording CA1 and CA3 apical fEPSPs generated by stimulation of oppositely oriented Schaffer collateral and mossy fiber axons, respectively, during DCS. Finally, nonsynaptic excitatory signal propagation was measured along antidromically stimulated CA1 axons at different DCS amplitudes and polarity. We find that modulation of both the fEPSP and population spike depends on axonal orientation relative to the electric field vector. Axonal orientation determines whether the DC field is excitatory or inhibitory and dendritic orientation affects the magnitude, but not the overall direction, of the DC effect. These data suggest that tDCS may oppositely affect neurons in a stimulated cortical volume if these neurons are excited by oppositely orientated axons in a constant electrical field.

A new measurement protocol of direct current resistivity data

Geophysics ◽  
2016 ◽  
Vol 81 (2) ◽  
pp. A7-A11 ◽  
Author(s):  
Jung-Ho Kim ◽  
Robert Supper ◽  
David Ottowitz ◽  
Birgit Jochum ◽  
Myeong-Jong Yi
Keyword(s):  
Direct Current ◽  
Current Injection ◽  
Potential Difference ◽  
Dc Resistivity ◽  
Weighting Method ◽  
Subsurface Structures ◽  
Resistivity Data ◽  
Measurement Protocol ◽  
Resistivity Inversion ◽  
Self Potential

We have developed a new protocol for measuring direct current (DC) resistivity data, in which self-potential (SP) data were measured immediately prior to obtaining the resistivity data. Based on this SP measurement, we have defined two different resistances: the forward resistance (i.e., a normalized potential difference caused by forward current injection) and the backward resistance (i.e., a normalized potential difference caused by backward current injection). This has allowed us to quantify distortions in the DC resistivity potential field caused by all unknown mechanisms, including ambient noises. In accordance with the proposed measurement protocol, we further devised a data-weighting method in a resistivity inversion for calculating more reasonable subsurface structures, and the method was based on the forward and backward resistances. Through inversion experiments using field resistivity data acquired by the proposed protocol, we have determined the validity and effectiveness of the proposed method.

Depth of investigation of collinear electrode arrays over homogeneous anisotropic half‐space in direct current methods

Geophysics ◽  
1981 ◽  
Vol 46 (5) ◽  
pp. 768-780 ◽  
Author(s):  
B. B. Bhattacharya ◽  
M. K. Sen
Keyword(s):  
Half Space ◽  
Direct Current ◽  
Inverse Relationship ◽  
Electrode Arrays ◽  
Definition Of ◽  
Depth Of Investigation

The definition of depth of investigation as suggested by Evjen (1938) [subsequently used by Roy and Apparao (1971) also for the study of depth of investigation of electrode arrays in direct current methods for homogeneous isotropic earth] has been used to study the depth of investigation of various collinear electrode arrays for a homogeneous anisotropic half‐space. It has been shown that some simple transformations are to be applied to the expressions of normalized depth of investigation characteristic (NDIC) of the same arrays over homogeneous isotropic earth to obtain normalized depth of investigation characteristic of various arrays placed over homogeneous anisotropic earth. The novelty of anisotropy is that the depth of investigation of collinear electrode arrays over homogeneous anisotropic half‐space bears an inverse relationship with the coefficient of anisotropy and also depends upon array length and dip of the plane of stratification. The effect of the coefficient of anisotropy is most pronounced for horizontally stratified anisotropic earth and is independent of it for vertically stratified anisotropic earth—entirely consistent with the concept of the “;paradox of anisotropy.” The depth of investigation of all the collinear arrays for inclined stratification lies somewhere between the values obtained for horizontal and vertical stratifications.

scholarly journals Investigation of Different Iontophoretic Currents Profiles for Short-Term Applications in Cosmetics

Pharmaceutics ◽  
2018 ◽  
Vol 10 (4) ◽  
pp. 266
Author(s):  
Jennyfer Cázares-Delgadillo ◽  
Lien Planard-Luong ◽  
Sébastian Gregoire ◽  
César Serna-Jiménez ◽  
Mayank Singhal ◽  
...  
Keyword(s):  
Direct Current ◽  
Pulse Current ◽  
Skin Penetration ◽  
Electrical Current ◽  
Current Profile ◽  
Active Ingredients ◽  
Ionization State ◽  
Enhancement Method ◽  
The Impact

This study aimed at investigating the effect of electrical current profile upon the iontophoretic transport of (i) ascorbic acid (AA) and (ii) ellagic acid (EA), into porcine skin in vitro, and the impact of the physicochemical properties of both actives on their mechanism of transport when formulated in cosmetic compositions. The experiments were performed using a proprietary iontophoretic device containing a roller to apply the formulation. Three current profiles were tested: (i) galvanic direct current (DC), (ii) square unipolar pulse current (SPC), and (iii) galvanic direct current (DC) + pulse current (PC). The skin samples were collected at different sampling points, extracted and analyzed by HPLC. Results suggested that the DC + PC mode for only 5 min was able to significantly increase the delivery of AA from o/w cosmetic compositions. The use of this current profile might improve the skin penetration of AA due to electromigration and passive diffusion, the latter being facilitated by the physical enhancement method. The SPC mode significantly improved the passage of EA in its neutral form from cosmetic o/w formulations by electroosmosis. Tailoring specific electrical current modes considering the ionization state of active ingredients would allow the design of short and personalized cosmetic treatments that significantly improve the penetration efficiency of the active ingredients and possibly reduce the doses applied.

Sign in / Sign up

Export Citation Format

Share Document