scholarly journals Low-frequency electromagnetic measurements as a zero-time discriminant of nuclear and chemical explosions -- OSI research final report

1996 ◽  
Author(s):  
J.J. Sweeney
Keyword(s):  
Low Frequency ◽  
Final Report ◽  
Electromagnetic Measurements ◽  
Chemical Explosions ◽  
Zero Time

scholarly journals Low frequency RF current drive. Final report, January 1, 1988--May 31, 1997

1999 ◽  
Author(s):  
N. Hershkowitz
Keyword(s):  
Low Frequency ◽  
Current Drive ◽  
Final Report

scholarly journals Coupled models in low-frequency electromagnetic simulation LDRD Final Report 94-ERI-004

1997 ◽  
Author(s):  
D.W. Hewett ◽  
D. Bateson ◽  
M. Gibbons ◽  
M. Lambert ◽  
L. Tung ◽  
...  
Keyword(s):  
Low Frequency ◽  
Electromagnetic Simulation ◽  
Final Report ◽  
Coupled Models

Tuning to Interaural Time Difference and Frequency Differs Between the Auditory Arcopallium and the External Nucleus of the Inferior Colliculus

2009 ◽  
Vol 101 (5) ◽  
pp. 2348-2361 ◽  
Author(s):  
Katrin Vonderschen ◽  
Hermann Wagner
Keyword(s):  
Inferior Colliculus ◽  
Tuning Curve ◽  
Interaural Time Difference ◽  
Low Frequency ◽  
Steep Slope ◽  
Time Difference ◽  
Interaural Time Differences ◽  
Tuning Curves ◽  
Barn Owls ◽  
Zero Time

Barn owls process sound-localization information in two parallel pathways, the midbrain and the forebrain pathway. Exctracellular recordings of neural responses to auditory stimuli from far advanced stations of these pathways, the auditory arcopallium in the forebrain and the external nucleus of the inferior colliculus in the midbrain, demonstrated that the representations of interaural time difference and frequency in the forebrain pathway differ from those in the midbrain pathway. Specifically, low-frequency representation was conserved in the forebrain pathway, while it was lost in the midbrain pathway. Variation of interaural time difference yielded symmetrical tuning curves in the midbrain pathway. By contrast, the typical forebrain-tuning curve was asymmetric with a steep slope crossing zero time difference and a less-steep slope toward larger contralateral time disparities. Low sound frequencies contributed sensitivity to contralateral leading sounds underlying these asymmetries, whereas high frequencies enhanced the steepness of slopes at small interaural time differences. Furthermore, the peaks of time-disparity tuning curves were wider in the forebrain than in the midbrain. The distribution of the steepest slopes of best interaural time differences in the auditory arcopallium, but not in the external nucleus of the inferior colliculus, was centered at zero time difference. The distribution observed in the auditory arocpallium is reminiscent of the situation observed in small mammals. We speculate that the forebrain representation may serve as a population code supporting fine discrimination of central interaural time differences and coarse indication of laterality of a stimulus for large interaural time differences.

Decomposition of electromagnetic fields into upgoing and downgoing components

Geophysics ◽  
2006 ◽  
Vol 71 (5) ◽  
pp. G211-G223 ◽  
Author(s):  
Lasse Amundsen ◽  
Lars Løseth ◽  
Rune Mittet ◽  
Svein Ellingsrud ◽  
Bjørn Ursin
Keyword(s):  
Synthetic Data ◽  
Low Frequency ◽  
Real Data ◽  
Sea Surface ◽  
Linear Phase ◽  
Electric Permittivity ◽  
The Real ◽  
Electromagnetic Data ◽  
Electromagnetic Measurements ◽  
Em Field

This paper gives a unified treatment of electromagnetic (EM) field decomposition into upgoing and downgoing components for conductive and nonconductive media, where the electromagnetic data are measured on a plane in which the electric permittivity, magnetic permeability, and electrical conductivity are known constants with respect to space and time. Above and below the plane of measurement, the medium can be arbitrarily inhomogeneous and anisotropic. In particular, the proposed decomposition theory applies to marine EM, low-frequency data acquired for hydrocarbon mapping where the upgoing components of the recorded field guided and refracted from the reservoir, that are of interest for the interpretation. The direct-source field, the refracted airwave induced by the source, the reflected field from the sea surface, and mostmagnetotelluric noise traveling downward just below the seabed are field components that are considered to be noise in electromagnetic measurements. The viability and validity of the decomposition method is demonstrated using modeled and real marine EM data, also termed seabed logging (SBL) data. The synthetic data are simulated in a model that is fairly representative of the geologic area where the real SBL were collected. The results from the synthetic data study therefore are used to assist in the interpretation of the real data from an area with [Formula: see text] water depth above a known gas province offshore Norway. The effect of the airwave is seen clearly in measured data. After field decomposition just below the seabed, the upgoing component of the recorded electric field has almost linear phase, indicating that most of the effect of the airwave component has been removed.

scholarly journals Sensitivity analysis for the appraisal of hydrofractures in horizontal wells with borehole resistivity measurements

Geophysics ◽  
2013 ◽  
Vol 78 (4) ◽  
pp. D209-D222 ◽  
Author(s):  
David Pardo ◽  
Carlos Torres-Verdín
Keyword(s):  
High Frequency ◽  
Horizontal Well ◽  
Low Frequency ◽  
Horizontal Wells ◽  
Hydraulic Fractures ◽  
Electrically Conductive ◽  
Resistivity Measurements ◽  
Electromagnetic Measurements ◽  
Open Hole ◽  
Thin Disks

We numerically evaluate the possibility of using borehole electromagnetic measurements to diagnose and quantify hydraulic fractures that have been artificially generated in a horizontal well. Hydrofractures are modeled as thin disks perpendicular to the well and filled with either sand-based or electrically conductive proppant. The study focuses on the effect of thickness and length (radius) of hydrofractures to assess their effects on specific configurations of borehole-resistivity instruments. Numerical results indicate that several measurements (e.g., those obtained with low- and high-frequency solenoids) could be used to assess the thickness of a fracture. However, only low-frequency measurements performed with electrodes and large-spacing between transmitter and receivers (18 m) exhibit the necessary sensitivity to reliably and accurately estimate the length of long hydrofractures (up to 150 m) in open-hole wells. In the case of steel-cased wells, the casing acts as a long electrode, whereby conventional low-frequency short-spaced, through-casing measurements are suitable for the accurate diagnosis of long hydrofractures (up to 150 m in length).

Use of low-frequency magnetoacoustic resonance in electromagnetic measurements

1984 ◽  
Vol 27 (2) ◽  
pp. 169-173
Author(s):  
L. N. Gubanova ◽  
E. D. Koltik ◽  
Yu. V. Tarbeev
Keyword(s):  
Low Frequency ◽  
Electromagnetic Measurements
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