A STUDY IN INDUCED POLARIZATION

Induced polarization in pyritic sandstone arises in part from overvoltage effects and in part from electrolytic polarization. Because induced‐polarization measurements are commonly used to search for sulfides, the electrolytic polarization is an undesirable background effect. Pyrite in sandstone can be located only when overvoltage polarization substantially exceeds electrolytic polarization. Laboratory measurements indicate this is true only if there is ten percent or more pyrite in a rock. However, overvoltage polarization is much larger when low current densities are used, particularly if the matrix resistivity is high. Field measurements indicate that at low current densities as little as one or two percent pyrite may provide sufficient overvoltage polarization to be recognizable in the presence of electrolytic polarization.

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A special circumstance of airborne induced‐polarization measurements

Geophysics ◽

10.1190/1.1443957 ◽

1996 ◽

Vol 61 (1) ◽

pp. 66-73 ◽

Cited By ~ 34

Author(s):

Richard S. Smith ◽

Jan Klein

Keyword(s):

Time Domain ◽

Eddy Currents ◽

High Arctic ◽

Induced Polarization ◽

Laboratory Measurements ◽

Dielectric Polarization ◽

Special Circumstance ◽

Polarization Measurements ◽

Airborne Electromagnetic

Airborne induced‐polarization (IP) measurements can be obtained with standard time‐domain airborne electromagnetic (EM) equipment, but only in the limited circumstances when the ground is sufficiently resistive that the normal EM response is small and when the polarizability of the ground is sufficiently large that the IP response can dominate the EM response. Further, the dispersion in conductivity must be within the bandwidth of the EM system. One example of what is hypothesized to be IP effects are the negative transients observed on a GEOTEM® survey in the high arctic of Canada. The dispersion in conductivity required to explain the data is very large, but is not inconsistent with some laboratory measurements. Whether the dispersion is caused by an electrolytic or dielectric polarization is not clear from the limited ground follow‐up, but in either case the polarization can be considered to be induced by eddy currents associated with the EM response of the ground. If IP effects are the cause of the negative transients in the GEOTEM data, then the data can be used to estimate the polarizabilities in the area.

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RECENT ADVANCES AND APPLICATIONS IN COMPLEX RESISTIVITY MEASUREMENTS

Geophysics ◽

10.1190/1.1440572 ◽

1975 ◽

Vol 40 (5) ◽

pp. 851-864 ◽

Cited By ~ 67

Author(s):

Kenneth L. Zonge ◽

Jeffrey C. Wynn

Keyword(s):

Host Rock ◽

Electromagnetic Coupling ◽

Field Measurements ◽

Complete Removal ◽

Induced Polarization ◽

Laboratory Measurements ◽

Spectral Measurements ◽

Complex Resistivity ◽

Geophysical Interpretation ◽

Rock Alteration

Several years of accumulating complex resistivity spectral measurements have indicated that there are still many unexplored areas in induced polarization surveying that need to be investigated for a more complete understanding of the polarization process. In addition to providing mineral discrimination capabilities, complex resistivity spectra can be used to differentiate between various barren host rock responses, to facilitate the complete removal of electromagnetic coupling, and to identify pipeline, fence, and various other cultural coupling effects. Results of field measurements are presented in an effort to demonstrate the utility of and necessity for making complete spectral measurements for serious geophysical interpretation. Correlation of field measurements with laboratory measurements on core samples from the same area demonstrates that strong electromagnetic coupling can be accurately removed from complete spectra without removing the important rock response. Recent field and laboratory measurements indicate that most, if not all, induced polarization responses attributed to magnetite are not really due to this mineral but can be traced to a host rock alteration response. Also, characteristic host rock signatures for sulfide environments appear to vary according to locality and type of deposits making it impossible to provide a universal set of signatures for sulfide deposits.

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Study of segregation in La1.8Sr0.2CuO4 superconductor by STEM-EDS microanalysis

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100125294 ◽

1987 ◽

Vol 45 ◽

pp. 54-55

Author(s):

T. F. Kelly ◽

P. J. Lee ◽

E. E. Hellstrom ◽

D. C. Larbalestier

Keyword(s):

Rare Earth ◽

High Field ◽

Transport Current ◽

Total Thickness ◽

New Class ◽

Ceramic Superconductors ◽

Current Densities ◽

Group Ii ◽

Eds Microanalysis

Recently there has been much excitement over a new class of high Tc (>30 K) ceramic superconductors of the form A1-xBxCuO4-x, where A is a rare earth and B is from Group II. Unfortunately these materials have only been able to support small transport current densities 1-10 A/cm2. It is very desirable to increase these values by 2 to 3 orders of magnitude for useful high field applications. The reason for these small transport currents is as yet unknown. Evidence has, however, been presented for superconducting clusters on a 50-100 nm scale and on a 1-3 μm scale. We therefore planned a detailed TEM and STEM microanalysis study in order to see whether any evidence for the clusters could be seen.A La1.8Sr0.2Cu04 pellet was cut into 1 mm thick slices from which 3 mm discs were cut. The discs were subsequently mechanically ground to 100 μm total thickness and dimpled to 20 μm thickness at the center.

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Saturated Hydraulic Conductivity of Clayey Tills and the Role of Fractures

Hydrology Research ◽

10.2166/nh.1990.0009 ◽

1990 ◽

Vol 21 (2) ◽

pp. 119-132 ◽

Cited By ~ 48

Author(s):

Johnny Fredericia

Keyword(s):

Hydraulic Conductivity ◽

American Studies ◽

Field Measurements ◽

Present Knowledge ◽

Saturated Hydraulic Conductivity ◽

Field Observations ◽

Laboratory Measurements ◽

Vertical Hydraulic Conductivity ◽

Data Field

The background for the present knowledge about hydraulic conductivity of clayey till in Denmark is summarized. The data show a difference of 1-2 orders of magnitude in the vertical hydraulic conductivity between values from laboratory measurements and field measurements. This difference is discussed and based on new data, field observations and comparison with North American studies, it is concluded to be primarily due to fractures in the till.

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High‐field measurements of anisotropy ofHc2and effect on grain‐boundary flux pinning in V3Si

Applied Physics Letters ◽

10.1063/1.89943 ◽

1978 ◽

Vol 32 (2) ◽

pp. 122-123 ◽

Cited By ~ 25

Author(s):

S. Foner ◽

E. J. McNiff

Keyword(s):

Grain Boundary ◽

Flux Pinning ◽

High Field ◽

Field Measurements ◽

Boundary Flux

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Aerosol Properties and Processes: A Path from Field and Laboratory Measurements to Global Climate Models

Bulletin of the American Meteorological Society ◽

10.1175/bams-88-7-1059 ◽

2007 ◽

Vol 88 (7) ◽

pp. 1059-1084 ◽

Cited By ~ 170

Author(s):

Steven J. Ghan ◽

Stephen E. Schwartz

Keyword(s):

Climate Models ◽

Global Climate ◽

Field Measurements ◽

Substantial Improvement ◽

Global Climate Models ◽

Department Of Energy ◽

Lower Atmosphere ◽

Laboratory Measurements ◽

Successive Generations ◽

Aerosol Properties

Aerosol particles in the lower atmosphere exert a substantial influence on climate and climate change through a variety of complex mechanisms. Consequently, there is a need to represent these influences in global climate models, and models have begun to include representations of these influences. However, the present treatment of aerosols in global climate models is highly simplified, omitting many processes and feedbacks that are thought to be climatically important. Thus, there is need for substantial improvement. Here we describe the strategy of the U.S. Department of Energy for improving representation of the properties, processes, and effects of tropospheric aerosols in global climate models. The strategy begins with a foundation of field and laboratory measurements that provide the basis for modules describing specific aerosol properties and processes. These modules are then integrated into regional aerosol models, which are evaluated by comparison with field measurements. Issues of scale are then addressed so that the modules can be applied to global aerosol models, which are evaluated by comparison with satellite retrievals and other observations. Finally, the validated set of modules is applied in global climate models for multicentury simulations. This strategy is expected to be applied to successive generations of global climate models.

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USB-based radiation monitor

Nuclear Technology and Radiation Protection ◽

10.2298/ntrp0602073d ◽

2006 ◽

Vol 21 (2) ◽

pp. 73-78 ◽

Cited By ~ 3

Author(s):

Vujo Drndarevic ◽

Nenad Jevtic ◽

Radivoje Djuric

Keyword(s):

Gamma Probe ◽

Field Measurements ◽

Laboratory Measurements ◽

Laptop Computer ◽

Universal Serial Bus ◽

Peripheral Device ◽

Radiation Monitor ◽

Labview Software ◽

Flexible Instrument ◽

Usb Bus

The Universal Serial Bus has become a dominant interface for the connection of standard peripheral devices to a PC computer. This paper analyzes the possibilities of USB bus applications in the field of measurement and environmental monitoring. As a result, a gamma radiation monitor consisting of an USB-based universal peripheral device and a gamma probe with a GM counter, has been designed. For the interfacing monitor with the powerful and easy to use LabVIEW software package, an instrument driver as a set of virtual instruments has been developed. The proposed monitor is a flexible instrument which can be used for laboratory measurements, as an environ mental radiation monitor or for training purposes. Connected to the laptop computer, the monitor becomes a portable instrument suitable for field measurements. Basic measurements and functionality properties of the radiation monitor are presented here.

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