Conventional Direct Current Method Research Articles

Improved Thomson Coefficient Measurements Using an AC Method

ABSTRACTWe present an improved AC (Alternating Current) method for the determination of the Thomson coefficient, which can be used for obtaining the absolute Seebeck coefficient. While previous work has focused on DC (Direct Current) methods, we analyze the influence of an AC current in order to derive the Thomson coefficient of a thin wire from measurable quantities. Our expression requires five parameters including AC current, resistance, temperature gradient, and the temperature changes due to the Thomson and Joule effects. Thus, a prior determination of thermal conductivity and sample geometry is not required, unlike DC methods. In order to validate our analysis, the Thomson coefficient of a thin Pt wire has been measured at several frequencies. The results agree with those obtained from a conventional DC method.

Sub-seafloor resistivity sensing using a vertical electrode configuration

There is growing interest in marine direct current (DC) resistivity methods for sub-seafloor exploration of a broad range of geophysical and geological targets. To address this, we have developed a new marine DC method with a vertical electrode configuration (VEC). Compared to conventional marine DC methods that use a horizontal electrode configuration, the shape and position of our VEC cable can be controlled relatively easily. Therefore, the VEC is suitable for operations in regions of steep bathymetry and for expeditious sub-seafloor resistivity exploration. In this study, we introduce a water-resistant electrode array cable and an onshore multichannel DC measurement system for stable and rapid data acquisition. To evaluate the performance and efficiency of the new system, we conducted field experiments in the shallow water zone at Shimizu Port, Suruga Bay, Japan. In order to quantitatively analyze the VEC-DC data, we adopt a 1-D numerical modeling code that computes the electric potential and apparent resistivity generated by a point and dipole current source used in the VEC-DC measurement. These can be placed at any position with an arbitrary electrode configuration in a multilayered space, including seawater and sub-seafloor layers. We also develop an inversion code for the VEC-DC data based on a simulated annealing (SA) optimization and applied this to the field data. The observed data is of sufficiently good quality to be used for inversion, and the SA result demonstrates that the proposed VEC-DC system is able to estimate the sub-seafloor resistivity structure.

Observations in trapping characteristics of positive bias temperature instability on high-k/metal gate n-type metal oxide semiconductor field effect transistor with the complementary multi-pulse technique

The trapping characteristics of positive bias temperature instability (PBTI) on a high-k/metal gate n-type metal oxide semiconductor field effect transistor (nMOSFET) have been investigated with a complementary multi-pulse technique (CMPT) in detail. With the CMPT technique, we found the threshold voltage shifts after PBTI are higher than that with the conventional direct current method, and the thickness of the SiO 2 interfacial layer has a significant effect on the measured results. The observation of these new results is attributed to the CMPT technique has the unique feature of effectively reducing the detrapping effect induced by the large bulk traps existed in high-k dielectrics. Besides, based on the results, the mechanism of PBTI in metal gate/high-k nMOSFETs is re-modeled.

Comparison of electrodermal constant voltage and constant current recording techniques using the phase angle between alternating voltage and current

If electrodermal activity is recorded with direct current, constant voltage and constant current measurements result in different dependencies of electrodermal reactions on the actual electrodermal level. The present study demonstrates empirically that such a problem does not exist when instead the phase angle changes between alternating current and voltage are obtained. Forty subjects were subjected to a 20-trial habituation series on two different occasions, in which electrodermal level variations were induced by room temperature changes. A multiplexing system was used to enable quasi-simultaneous constant current and constant voltage recording under both direct and alternating current measurement conditions. If the alternating current technique was applied and electrodermal responses were expressed as changes of phase angle between voltage and current, electrodermal recordings with constant voltage and with constant current provided equivalent results, even if electrodermal levels were considerably different. Therefore, using the phase angle method instead of the conventional direct current methods will finally resolve the problem of differential level dependency in electrodermal recording. A further advantage will be that electrode and skin polarization are prevented by the use of alternating current.

Comparison of electrodermal constant voltage and constant current recording techniques using the phase angle between alternating voltage and current

If electrodermal activity is recorded with direct current, constant voltage and constant current measurements result in different dependencies of electrodermal reactions on the actual electrodermal level. The present study demonstrates empirically that such a problem does not exist when instead the phase angle changes between alternating current and voltage are obtained. Forty subjects were subjected to a 20-trial habituation series on two different occasions, in which electrodermal level variations were induced by room temperature changes. A multiplexing system was used to enable quasi-simultaneous constant current and constant voltage recording under both direct and alternating current measurement conditions. If the alternating current technique was applied and electrodermal responses were expressed as changes of phase angle between voltage and current, electrodermal recordings with constant voltage and with constant current provided equivalent results, even if electrodermal levels were considerably different. Therefore, using the phase angle method instead of the conventional direct current methods will finally resolve the problem of differential level dependency in electrodermal recording. A further advantage will be that electrode and skin polarization are prevented by the use of alternating current.

Pulsed direct current iontophoresis as a possible new treatment for hyperhidrosis

Tap water iontophoresis with direct current represents the therapy of choice in palmoplantar hyperhidrosis. Side effects are minor discomfort and skin irritations. Improper use may induce iontophoretic burns at sites of minor skin injuries. The aim of this study was to find ways of minimizing side effects, increasing safety standards and reducing the technical complications of tap water iontophoresis without loss of efficacy. In a blind study, 30 patients with palmar hyperhidrosis were treated with tap water iontophoresis using pulsed direct current of 4.3 kHz or 10.0 kHz. Efficacy and side effects were compared with those of the conventional direct current method as a control. Normal sweat secretion rates of palms were found after an average of ten treatment sessions with the conventional direct current method and after twelve with pulsed direct current of 4.3 or 10 kHz. Treatment with pulsed direct current of 4.3 kHz failed to inhibit palmar hyperhidrosis in two of ten patients. Occasionally, such side effects as discomfort, skin irritation, and mild electric shock occurred when direct current was applied. Using pulsed direct current subjective sensations of discomfort and skin irritation were rare (4.3 kHz) or very rare (10 kHz). Electric shock was completely prevented. Because of the minimal side effects, despite minor loss of efficacy tap water iontophoresis with pulsed direct current can be a valuable alternative treatment for palmar hyperhidrosis.

Relative performances of central and dipole frequency soundings over a layered earth

Variable frequency soundings in the audio-range replaces shallow conventional direct current methods for determination of layer parameters when surface layer resistivity is high. Central frequency soundings (CFS) is one such method that involves measurement of the existing vertical magnetic field component induced at the centre of a horizontal circular or square loop. Dipole method of frequency sounding using small horizontal coplanar loops (abbreviated DFS) measuring the same field component is also considered. Theoretical studies on CFS and DFS over two- and three-layer horizontally stratified earth are carried out and the response characteristics computed and analysed.