Improved impedance conditions for a thin layer problem in a nonsmooth domain

2019 ◽  
Vol 42 (5) ◽  
pp. 1432-1448
Author(s):  
Alexis Auvray ◽  
Grégory Vial
Keyword(s):  
Thin Layer ◽  
Nonsmooth Domain ◽  
Impedance Conditions ◽  
Layer Problem

COMPARISON OF AIRBORNE EM COIL SYSTEMS PLACED OVER A MULTILAYER CONDUCTING EARTH

Geophysics ◽  
1973 ◽  
Vol 38 (5) ◽  
pp. 894-919 ◽  
Author(s):  
Ajit K. Sinha
Keyword(s):  
Thin Layer ◽  
Computer Program ◽  
Relative Effectiveness ◽  
Single Frequency ◽  
Master Curves ◽  
Airborne Electromagnetic ◽  
Hidden Layer ◽  
Static Conditions ◽  
Airborne Em ◽  
Layer Problem

A detailed analysis has been made on the relative effectiveness of the four types of coil arrangements used in airborne electromagnetic surveying for the mapping of subsurface inhomogeneities. By comparing the theoretical responses for the four systems over known geologic sections, it has been established that the horizontal coplanar system is the most effective for detecting inhomogeneities in single‐frequency airborne surveys and produces the largest anomaly in multifrequency work. The next largest anomaly in both the cases is obtained in the vertical coplanar arrangement. The multilayer computer program used to derive the theoretical master curves for comparing the performance of the four systems is completely general except for our assumption of the quasi‐static conditions, which is justified in all geophysical induction problems. A study of the “hidden‐layer problem” to determine the best system and conditions for detection of a thin layer sandwiched between two thicker beds has been made with the help of the program. Horizontal coplanar and vertical coplanar systems are again found to be the best and second best systems, respectively, for their detection. It is also clear that a conductive sandwiched bed is much easier to detect than a resistive one.

Applications of Photoelectron Microscopy

1976 ◽  
Vol 34 ◽  
pp. 506-507
Author(s):  
William J. Baxter
Keyword(s):  
Electron Microscopy ◽  
Thermal Decomposition ◽  
Chemical Composition ◽  
Ultraviolet Radiation ◽  
Thin Layer ◽  
Edge Effects ◽  
Electron Optics ◽  
Surface Layers ◽  
Crystalline Orientation ◽  
Fluorescent Screen

In this form of electron microscopy, photoelectrons emitted from a metal by ultraviolet radiation are accelerated and imaged onto a fluorescent screen by conventional electron optics. image contrast is determined by spatial variations in the intensity of the photoemission. The dominant source of contrast is due to changes in the photoelectric work function, between surfaces of different crystalline orientation, or different chemical composition. Topographical variations produce a relatively weak contrast due to shadowing and edge effects.Since the photoelectrons originate from the surface layers (e.g. ∼5-10 nm for metals), photoelectron microscopy is surface sensitive. Thus to see the microstructure of a metal the thin layer (∼3 nm) of surface oxide must be removed, either by ion bombardment or by thermal decomposition in the vacuum of the microscope.

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