scholarly journals Examples of ac resistivity prospecting in archaeological research

1998 ◽  
Vol 41 (3) ◽  
Author(s):  
P. Mauriello ◽  
D. Monna ◽  
I. Bruner
Keyword(s):  
Skin Effect ◽  
Dipole Source ◽  
Electrode Polarization ◽  
Archaeological Research ◽  
Frequency Range ◽  
Buried Structures ◽  
Resistivity Survey ◽  
Resistivity Tensor ◽  
Straight Lines ◽  
Self Potential

In this paper we present the results of an alternating current resistivity survey, with a view to future tomographic processing. Two examples are given to evaluate the validity and the resolution of the method. The first in the Sabine Necropolis of Colle del Forno (Montelibretti, Rome), the second in the Etruscan settlement of Poggio Colla (Vicchio, Florence). All the measurements were carried out utilising current up to 512 Hz and a mobile dipole MN along straight lines, having two fixed current probes A and B. It was found that skin effect is uninfluential in the frequency range adopted. Given the absence of natural or artificial disturbances in the signal (e.g. electrode polarization and self potential), it was possible to perform very fast measurements with two operators only. Moreover, the use of a multiple dipole source configuration allows the calculation of the determinant of the apparent resistivity tensor. In the examples shown, this parameter detects the actual position of buried structures independently of the direction of the electric sources.

The self‐potential method in the geothermal exploration of Greece

Geophysics ◽  
1997 ◽  
Vol 62 (6) ◽  
pp. 1715-1723 ◽  
Author(s):  
George Apostolopoulos ◽  
Ioannis Louis ◽  
Evangelos Lagios
Keyword(s):  
Surrounding Medium ◽  
Geophysical Methods ◽  
Low Frequency ◽  
Potential Method ◽  
Geothermal System ◽  
Electrode Polarization ◽  
Geothermal Exploration ◽  
Contour Maps ◽  
Tectonic Features ◽  
Self Potential

Self‐potential (SP) anomalies are generated by flows of fluid, heat, and ions in the earth. SP investigations have been used to locate and delineate sources associated with such flows in three areas of geothermal interest in Greece—Lesvos Island, Loutra Hypatis (central Greece), and Nisyros Island. A combination of geophysical methods, with SP being the primary method, has been applied in these areas. The SP method is adversely influenced by various sources of noise. Field procedures have been suggested to minimize their effects by monitoring electrode polarization and telluric activity. The interpretation of SP contour maps is preferred to using profile data. A procedure was adopted for SP interpretation, and the results were satisfactory. However, this model is based on thermoelectric sources only and is not related directly to hot fluid movement. In all three survey areas, the geothermal zones delimited by the SP interpretation in combination with data acquired by other geophysical methods result in an integrated interpretation of the geothermal system. Since SP and very‐low‐frequency (VLF) anomalies can be generated by the same geological source (i.e., geothermal, highly conductive zone), the corresponding results are compared to provide a strong indication of the presence of geothermal zones. The activity of geothermal zones affects the conductivity of the surrounding medium, which also can be detected by dc resistivity and audio‐magnetotelluric (AMT) methods. In addition, geothermal zones can be related to various interfaces or tectonic features that can be detected by gravity or seismic methods.

Study on the Resistive Heat Source in a Two-Phase Medium at High-Frequency Electrosurgical Intervention

2017 ◽  
Vol 873 ◽  
pp. 140-144 ◽  
Author(s):  
Volodymyr Sydorets ◽  
Andrey Dubko ◽  
Volodymyr Korzhyk
Keyword(s):  
Heat Source ◽  
High Frequency ◽  
Skin Effect ◽  
Wide Frequency Range ◽  
Copper Electrode ◽  
Two Dimensional ◽  
Frequency Range ◽  
Two Phase ◽  
Conducting Materials ◽  
Phase Medium

Numerical analysis of distribution of resistive heat source in two-phase conducting medium (copper electrode – biological tissue) was carried out. Axisymmetric two-dimensional elliptic problem, with boundary conditions of the first and second kind was solved in the environment of MATLAB mathematical package, using the method of finite differences. Analysis results show that heat source concentration and other parameters are determined by skin effect. This fact should be taken into account in development of new effective methods of surgical treatment and respective instruments. This mathematical model can be applied in a wide frequency range for conducting materials with different conductivities.

NON-UNIFORM SCALING BEHAVIOR IN SELF-POTENTIAL EARTHQUAKE-RELATED SIGNALS

2008 ◽  
Vol 08 (03n04) ◽  
pp. L261-L267 ◽  
Author(s):  
LUCIANO TELESCA ◽  
MICHELE LOVALLO ◽  
ALEJANDRO RAMIREZ-ROJAS ◽  
FERNANDO ANGULO-BROWN
Keyword(s):  
Nonstationary Time Series ◽  
Scaling Behavior ◽  
Fluctuation Analysis ◽  
Frequency Range ◽  
Scaling Properties ◽  
Time Dynamics ◽  
First Results ◽  
Detrended Fluctuation ◽  
Self Potential ◽  
Uniform Scaling

The scaling properties of the time dynamics of self-potential data (in the frequency range between 0 and 0.125Hz) observed in 1995 at Acapulco station in Mexico were investigated. On the basis of detrended fluctuation analysis (DFA), which is a powerful method to detect scaling in nonstationary time series, deviations from uniform power-law scaling were identified and quantified. Our results suggest that an evident non-uniform scaling behavior in self-potential data could be related to the occurrence on September 14, 1995 of the strongest earthquake. These first results could be useful in the framework of earthquake prediction studies.

scholarly journals The self‐potential method in geothermal exploration

Geophysics ◽  
1979 ◽  
Vol 44 (2) ◽  
pp. 226-245 ◽  
Author(s):  
Robert F. Corwin ◽  
Donald B. Hoover
Keyword(s):  
Potential Method ◽  
Source Model ◽  
Irreversible Thermodynamics ◽  
Electrode Polarization ◽  
Coupling Coefficients ◽  
Spherical Source ◽  
Analytical Technique ◽  
Thermal Fluids ◽  
Geothermal Activity ◽  
Self Potential

Laboratory measurements and field data indicate that self‐potential anomalies comparable to those observed in many areas of geothermal activity may be generated by thermoelectric or electrokinetic coupling processes. A study using an analytical technique based on concepts of irreversible thermodynamics indicates that, for a simple spherical source model, potentials generated by electrokinetic coupling may be of greater amplitude than those developed by thermoelectric coupling. Before more quantitative interpretations of potentials generated by geothermal activity can be made, analytical solutions for more realistic geometries must be developed, and values of in‐situ coupling coefficients must be obtained. If the measuring electrodes are not watered, and if telluric currents and changes in electrode polarization are monitored and corrections made for their effects, most self‐potential measurements are reproducible within about ±5 mV. Reproducible short‐wavelength geologic noise of as much as ±10 mV, primarily caused by variation in soil properties, is common in arid areas, with lower values in areas of uniform, moist soil. Because self‐potential variations may be produced by conductive mineral deposits, stray currents from cultural activity, and changes in geologic or geochemical conditions, self‐potential data must be analyzed carefully before a geothermal origin is assigned to observed anomalies. Self‐potential surveys conducted in a variety of geothermal areas show anomalies ranging from about 50 mV to over 2 V in amplitude over distances of about 100 m to 10 km. The polarity and waveform of the observed anomalies vary, with positive, negative, bipolar, and multipolar anomalies having been reported from different areas. Steep potential gradients often are seen over faults which are thought to act as conduits for thermal fluids. In some areas, anomalies several kilometers wide correlate with regions of known elevated thermal gradient or heat flow.

TSV Modeling Considering Signal Integrity Issues

2010 ◽  
Vol 2010 (1) ◽  
pp. 000572-000576
Author(s):  
Ivan Ndip ◽  
Brian Curran ◽  
Kai Löbbicke ◽  
Stephan Guttowski ◽  
Herbert Reichl ◽  
...  
Keyword(s):  
Slow Wave ◽  
Skin Effect ◽  
Signal Integrity ◽  
Semiconductor Structure ◽  
Frequency Range ◽  
Metal Insulator ◽  
Metal Insulator Semiconductor ◽  
Tem Mode ◽  
The Impact

Since a TSV has a metal-insulator-semiconductor structure, it supports three fundamental modes namely, skin-effect, slow-wave and dielectric quasi-TEM mode. In this contribution, we predict the frequency range of these modes, considering TSVs for interposer applications as an example. Furthermore, the impact of Si-resistivity on signal integrity is quantified and coaxial TSV configurations are proposed to minimize this impact.

scholarly journals The dielectric constant of sandstones, 60 kHz to 4 MHz

Geophysics ◽  
1987 ◽  
Vol 52 (5) ◽  
pp. 644-654 ◽  
Author(s):  
Rosemary J. Knight ◽  
Amos Nur
Keyword(s):  
Dielectric Constant ◽  
Surface Area ◽  
Dielectric Response ◽  
Water Saturation ◽  
Pore Space ◽  
Strong Dependence ◽  
Complex Impedance ◽  
Volume Ratio ◽  
Electrode Polarization ◽  
Frequency Range

Complex impedance data were collected for eight sandstones at various levels of water saturation [Formula: see text] in the frequency range of 5 Hz to 4 MHz. The measurements were made using a two‐electrode technique with platinum electrodes sputtered onto the flat faces of disk‐ shaped samples. Presentation of the data in the complex impedance plane shows clear separation of the response due to polarization at the sample‐electrode interface from the bulk sample response. Electrode polarization effects were limited to frequencies of less than 60 kHz, allowing us to study the dielectric constant κ′ of the sandstones in the frequency range of 60 kHz to 4 MHz. κ′ of all samples at all levels of saturation shows a clear power‐law dependence upon frequency. Comparing the data from the eight sandstones at [Formula: see text], the magnitude of the frequency dependence was found to be proportional to the surface area‐to‐volume ratio of the pore space of the sandstones. The surface area‐to‐volume ratio of the pore space of each sandstone was determined using a nitrogen gas adsorption technique and helium porosimetry. κ′ also exhibits a strong dependence on [Formula: see text]. κ′ increases rapidly with [Formula: see text] at low saturations, up to some critical saturation above which κ′ increases more gradually and linearly with [Formula: see text]. Using the surface area‐to‐volume ratios of the sandstones, the critical saturation in the dielectric response was found to correspond to water coverage of approximately 2 nm on the surface of the pore space. Our interpretation of the observed dependence of κ′ on both frequency and [Formula: see text] is that it is the ratio of surface water to bulk water in the pore space of a sandstone that controls the dielectric response through a Maxwell‐Wagner type of mechanism.

Domain Formation in Synthetic Quartz

1971 ◽  
Vol 29 ◽  
pp. 156-157
Author(s):  
Joseph J. Comer
Keyword(s):  
Electron Beam ◽  
Room Temperature ◽  
Domain Formation ◽  
Synthetic Quartz ◽  
Transmission Electron ◽  
Black Spots ◽  
Diffraction Mode ◽  
Domain Boundaries ◽  
Kikuchi Lines ◽  
Straight Lines

Domains visible by transmission electron microscopy, believed to be Dauphiné inversion twins, were found in some specimens of synthetic quartz heated to 680°C and cooled to room temperature. With the electron beam close to parallel to the [0001] direction the domain boundaries appeared as straight lines normal to <100> and <410> or <510> directions. In the selected area diffraction mode, a shift of the Kikuchi lines was observed when the electron beam was made to traverse the specimen across a boundary. This shift indicates a change in orientation which accounts for the visibility of the domain by diffraction contrast when the specimen is tilted. Upon exposure to a 100 KV electron beam with a flux of 5x 1018 electrons/cm2sec the boundaries are rapidly decorated by radiation damage centers appearing as black spots. Similar crystallographio boundaries were sometimes found in unannealed (0001) quartz damaged by electrons.

Sign in / Sign up

Export Citation Format

Share Document