|
Electrical Resistance Survey (archaeology)
Electrical resistance surveys (also called earth resistance or resistivity survey) are one of a number of methods used in archaeological geophysics, as well as in engineering geological investigations. In this type of survey electrical resistance meters are used to detect and map subsurface archaeological features and patterning. Overview Electrical resistance meters can be thought of as similar to the Ohmmeters used to test electrical circuits. Archaeological features can be mapped when they are of higher or lower resistivity than their surroundings. A stone foundation might impede the flow of electricity, while the organic deposits within a midden might conduct electricity more easily than surrounding soils. Although generally used in archaeology for planview mapping, resistance methods also have a limited ability to discriminate depth and create vertical profiles (see Electrical resistivity tomography). Further applications include the measurement of the electrical resistiv ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geophysical Survey (archaeology)
In archaeology, geophysical survey is ground-based physical sensing techniques used for archaeological imaging or mapping. Remote sensing and marine surveys are also used in archaeology, but are generally considered separate disciplines. Other terms, such as "geophysical prospection" and "archaeological geophysics" are generally synonymous. Overview Geophysical survey is used to create maps of subsurface archaeological features. Features are the non-portable part of the archaeological record, whether standing structures or traces of human activities left in the soil. Geophysical instruments can detect buried features when their physical properties contrast measurably with their surroundings. In some cases individual artifacts, especially metal, may be detected as well. Readings taken in a systematic pattern become a data set that can be rendered as image maps. Survey results can be used to guide excavation and to give archaeologists insight into the patterning of non-excavated ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrical Resistance
The electrical resistance of an object is a measure of its opposition to the flow of electric current. Its reciprocal quantity is , measuring the ease with which an electric current passes. Electrical resistance shares some conceptual parallels with mechanical friction. The SI unit of electrical resistance is the ohm (), while electrical conductance is measured in siemens (S) (formerly called the 'mho' and then represented by ). The resistance of an object depends in large part on the material it is made of. Objects made of electrical insulators like rubber tend to have very high resistance and low conductance, while objects made of electrical conductors like metals tend to have very low resistance and high conductance. This relationship is quantified by resistivity or conductivity. The nature of a material is not the only factor in resistance and conductance, however; it also depends on the size and shape of an object because these properties are extensive rather than intens ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Feature (archaeology)
In archaeological excavation, a feature is a collection of one or more contexts representing some human non-portable activity, such as a hearth or wall. Features serve as an indication that the area in which they are found has been interfered with in the past, usually by humans. Features are distinguished from artifacts in that they cannot be separated from their location without changing their form. Artifacts are portable, while features are non-portable. Artifacts and features can both be made from any available material, with the primary distinction being portability. Features and artifacts differ from ecofacts. Ecofacts are natural remains, such as plants and animals. Types Features are categorized by the time period, as either historic or prehistoric. Prehistoric archaeology refers to the time in history before human life was recorded or documented, while historic archaeology refers to the time period where there was a documented human past. In relation to site stra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrical Resistivity Tomography
Electrical resistivity tomography (ERT) or electrical resistivity imaging (ERI) is a geophysical technique for imaging sub-surface structures from electrical resistivity measurements made at the surface, or by electrodes in one or more boreholes. If the electrodes are suspended in the boreholes, deeper sections can be investigated. It is closely related to the medical imaging technique electrical impedance tomography (EIT), and mathematically is the same inverse problem. In contrast to medical EIT, however, ERT is essentially a direct current method. A related geophysical method, induced polarization (or spectral induced polarization), measures the transient response and aims to determine the subsurface chargeability properties. Electrical resistivity measurements can be used for identification and quantification of depth of groundwater, detection of clays, and measurement of groundwater conductivity. History The technique evolved from techniques of electrical prospecting th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrical Resistivity Measurement Of Concrete
Concrete electrical resistivity can be obtained by applying a current into the concrete and measuring the response voltage. There are different methods for measuring concrete resistivity. Laboratory methods Two electrodes Concrete electrical resistance can be measured by applying a current using two electrodes attached to the ends of a uniform cross-section specimen. Electrical resistivity is obtained from the equation: :\rho = R \frac, \,\! :''R'' is the electrical resistance of the specimen, the ratio of voltage to current (measured in ohms, Ω) :''\ell'' is the length of the piece of material (measured in metres, m) :''A'' is the cross-sectional area of the specimen (measured in square metres, m2). This method suffers from the disadvantage that contact resistance can significantly add to the measured resistance causing inaccuracy. Conductive gels are used to improve the contact of the electrodes with the sample. Four electrodes The problem of contact resistance can be over ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Res Survey
Res or RES may refer to: Sciences Computing *Russian and Eurasian Security Network * Spanish Supercomputing Network (''Red Española de Supercomputación'') Energy * RES - The School for Renewable Energy Science * US Renewable Electricity Standard *Renewable Energy Systems, a UK company Mathematics * Residue (complex analysis) function Medicine * Reticuloendothelial system, in anatomy Archaeology * Répertoire d'Épigraphie Sémitique, a journal publishing Semitic language inscriptions Latin word meaning "thing" * Entity (other) * Object (philosophy) *The first word of several Latin phrases: **''Res divina'' (''service of the gods'') **'' Res extensa'' Descartes' physical world **'' Res gestae'' (''Things done'') **'' Res inter alios acta'' (''A thing done between others'') **''Res ipsa loquitur'' (''The thing speaks for itself'') **''Res judicata'' (''A matter lreadyjudged'') **''Res nullius'' (''An unowned thing'') **'' Res publica'' (''A public t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrode Array
An electrode array is a configuration of electrodes used for measuring either an electric current or voltage. Some electrode arrays can operate in a bidirectional fashion, in that they can also be used to provide a stimulating pattern of electric current or voltage. Common arrays include: *Schlumberger (Wenner) *Wenner alpha *Wenner beta *Wenner gamma *Pole-pole *Dipole-dipole *Pole-dipole *Equatorial dipole-dipole Resistivity Resistivity measurement of bulk materials is a frequent application of electrode arrays. The figure shows a Wenner array, one of the possible ways of achieving this. Injecting the current through electrodes separate from those being used for measurement of potential has the advantage of eliminating any inaccuracies caused by the injecting circuit resistance, particularly the contact resistance between the probe and the surface, which can be high. Assuming the material is homogenous, the resistivity in the Wenner array is given by: :\rho=2 \pi a \frac w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wenner Electrode Array
An electrode array is a configuration of electrodes used for measuring either an electric current or voltage. Some electrode arrays can operate in a bidirectional fashion, in that they can also be used to provide a stimulating pattern of electric current or voltage. Common arrays include: *Schlumberger (Wenner) *Wenner alpha *Wenner beta *Wenner gamma *Pole-pole *Dipole-dipole *Pole-dipole *Equatorial dipole-dipole Resistivity Resistivity measurement of bulk materials is a frequent application of electrode arrays. The figure shows a Wenner array, one of the possible ways of achieving this. Injecting the current through electrodes separate from those being used for measurement of potential has the advantage of eliminating any inaccuracies caused by the injecting circuit resistance, particularly the contact resistance between the probe and the surface, which can be high. Assuming the material is homogenous, the resistivity in the Wenner array is given by: :\rho=2 \pi a \frac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wenner Array
An electrode array is a configuration of electrodes used for measuring either an electric current or voltage. Some electrode arrays can operate in a bidirectional fashion, in that they can also be used to provide a stimulating pattern of electric current or voltage. Common arrays include: *Schlumberger (Wenner) *Wenner alpha *Wenner beta *Wenner gamma *Pole-pole *Dipole-dipole *Pole-dipole *Equatorial dipole-dipole Resistivity Electrical resistivity and conductivity, Resistivity measurement of bulk materials is a frequent application of electrode arrays. The figure shows a Wenner array, one of the possible ways of achieving this. Injecting the current through electrodes separate from those being used for measurement of potential has the advantage of eliminating any inaccuracies caused by the injecting circuit resistance, particularly the contact resistance between the probe and the surface, which can be high. Assuming the material is homogenous, the resistivity in the Wenner arr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vertical Electrical Sounding
Vertical electrical sounding (VES) is a geophysical method for investigation of a geological medium. The method is based on the estimation of the electrical conductivity or resistivity of the medium. The estimation is performed based on the measurement of voltage of electrical field induced by the distant grounded electrodes (current electrodes). Measurements Figures 1–4 show the possible configuration of the measurement setup. The electrodes ''A'' and ''B'' are current electrodes which are connected to a current source; ''N'' and ''M'' are potential electrodes which are used for the voltage measurements. As source, the direct current or low frequency alternating current is used. The interpretation of the measurements can be performed based on the apparent resistivity values. The depth of investigation depends on the distance between the current electrodes. In order to obtain the apparent resistivity as the function of depth, the measurements for each position are performed w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
