ELECTROMAGNETIC COUPLING BETWEEN GROUNDED WIRES AT THE SURFACE OF A TWO‐LAYER EARTH

Geophysics ◽  
1973 ◽  
Vol 38 (5) ◽  
pp. 854-863 ◽  
Author(s):  
Gerald W. Hohmann
Keyword(s):  
Numerical Solution ◽  
Lower Layer ◽  
Electromagnetic Coupling ◽  
Induced Polarization ◽  
Electrode Configuration ◽  
Smooth Transition ◽  
Layer Model ◽  
The Earth ◽  
Two Layer Model

A technique has been developed for computing the effects of electromagnetic coupling in induced polarization surveys, when the earth can be approximated by a two‐layer model. Results are given for the dipole‐dipole array, but the numerical solution described can be applied to any electrode configuration. No unusual effects were observed for the models computed. As the thickness of the upper layer is increased, there is a smooth transition between the coupling response of a homogeneous earth having the resistivity of the upper layer and that of a homogeneous earth having a resistivity equal to that of the lower layer.

On the Thickness Ratio in the Quasigeostrophic Two-Layer Model of Baroclinic Instability

2013 ◽  
Vol 70 (5) ◽  
pp. 1505-1511 ◽  
Author(s):  
Noboru Nakamura ◽  
Lei Wang
Keyword(s):  
Growth Rate ◽  
Vertical Structure ◽  
Lower Layer ◽  
Baroclinic Instability ◽  
Thickness Ratio ◽  
Layer Model ◽  
Optimal Thickness ◽  
Zonal Wavenumber ◽  
The Mean ◽  
Two Layer Model

Abstract It is shown that the classical quasigeostrophic two-layer model of baroclinic instability possesses an optimal ratio of layer thicknesses that maximizes the growth rate, given the basic-state shear (thermal wind), beta, and the mean Rossby radius. This ratio is interpreted as the vertical structure of the most unstable mode. For positive shear and beta, the optimal thickness of the lower layer approaches the midheight of the model in the limit of strong criticality (shear/beta) but it is proportional to criticality in the opposite limit. For a set of parameters typical of the earth’s midlatitudes, the growth rate maximizes at a lower-layer thickness substantially less than the midheight and at a correspondingly larger zonal wavenumber. It is demonstrated that a turbulent baroclinic jet whose statistical steady state is marginally critical when run with equal layer thicknesses can remain highly supercritical when run with a nearly optimal thickness ratio.

scholarly journals Examining cerebral hemodynamics in a two-layer model of the human head using broadband near-infrared spectroscopy

2021 ◽  
Author(s):  
Olivia Pucci
Keyword(s):  
Optical Properties ◽  
Near Infrared ◽  
Continuous Wave ◽  
Lower Layer ◽  
Homogeneous Medium ◽  
Human Head ◽  
Cerebral Hemodynamics ◽  
Layer Model ◽  
Adult Human ◽  
Two Layer Model

The development of a continuous-wave method is presented, to quantify accurately the optical properties of a two-layer model of the human head using a broadband spectral approach. In particular, focus is put on the reconstruction of the absolute absorption and scattering properties of a two-layered phantom model of the human head with steady-state multi-distance measurements by performing differential fit analysis of the near-infrared (NIR) reflectance spectrum between 700 nm and 1000 nm. The two-layer model approximation was fitted to experimental broadband absorbance measurements obtained from two-layered phantoms with known optical properties. Results demonstrated that the suggested method was able to determine the optical properties of the lower layer with minimal error at specific source-detector distances. Preliminary results on the non-invasive measurement of the optical properties of the adult human brain in a two-layer approximation are presented. Finally, a mobile wireless NIR device is used to measure changes in the temporal characteristics of cerebral hemodynamic responses to functional brain activity, in particulaur the effect of smoking. Results suggest that assuming homogeneous medium for the adult human head severely underestimates the changes in cerebral hemodynamics. Hence, it is important to take surrounding layers into consideration when performing cerebral measurements using NIR spectroscopy.

scholarly journals Permanent bedforms in a theoretical model of wave-sea-bed interactions

2000 ◽  
Vol 7 (1/2) ◽  
pp. 31-35 ◽  
Author(s):  
J. M. Becker ◽  
D. Bercovici
Keyword(s):  
Theoretical Model ◽  
Nonlinear Response ◽  
External Surface ◽  
Lower Layer ◽  
Sea Waves ◽  
Layer Model ◽  
Periodic Forcing ◽  
Sea Bed ◽  
Two Layer Model ◽  
Large Wavelength

Abstract. The interaction between sea waves and a deformable sea-bed is studied with a simple two-layer model in which the upper-layer fluid is inviscid and the lower-layer fluid is bi-viscous to account for non-Newtonian behaviour of sand and sediments. The nonlinear response of the system to periodic forcing by an external surface pressure is determined. It is shown that a simple bi-viscous rheology allows small wavelength morphology in the lower layer to be generated from large wavelength surface waves in the upper inviscid layer, although the morphology is not permanent. For a bi-viscous rheology with a pressure-dependent yield stress (which accounts for the fact that sand yields less readily under loading than unloading), however, small wavelength and permanent features are formed in the seabed.

A two-layer model of Gulf Stream separation

1969 ◽  
Vol 39 (3) ◽  
pp. 511-528 ◽  
Author(s):  
A. T. Parsons
Keyword(s):  
Wind Stress ◽  
Gulf Stream ◽  
Stream Flow ◽  
Lower Layer ◽  
Western Boundary ◽  
Boundary Current ◽  
Layer Model ◽  
Layer Depth ◽  
Boundary Currents ◽  
Two Layer Model

A study is made of the wind-driven circulation of a two-layer ocean within a square basin, with a view to describing the observed separation of western boundary currents. The lower layer is allowed to surface and the line along which the upper-layer depth vanishes is interpreted as the region of the surfacing thermocline. For a representative wind stress the theory predicts the gross features of the Gulf Stream flow, the region adjacent to the surfacing line containing the separated boundary current. By assuming that the effects of friction and inertia are confined to regions of a boundary-layer character, the position of a separated current is shown to depend only on the degree of stratification and certain integral properties of the applied wind stress.

Induced‐polarization and electromagnetic modeling of a three‐dimensional body buried in a two‐layer anisotropic earth

Geophysics ◽  
1986 ◽  
Vol 51 (12) ◽  
pp. 2235-2246 ◽  
Author(s):  
Zonghou Xiong ◽  
Yanzhong Luo ◽  
Shoutan Wang ◽  
Guangyao Wu
Keyword(s):  
Integral Equation ◽  
Green’S Function ◽  
Green's Function ◽  
Lower Layer ◽  
Integral Equation Method ◽  
Induced Polarization ◽  
Equation Method ◽  
Frequency Effect ◽  
Electromagnetic Modeling ◽  
The Earth

The integral equation method is used for induced‐polarization (IP) and electromagnetic (EM) modeling of a finite inhomogeneity in a two‐layer anisotropic earth. An integral equation relates the exciting electric field and the scattering currents in the homogeneity through the electric tensor Green’s function deduced from the vector potentials in the lower layer of the earth. Digital linear filtering and three‐point parabolic Lagrangian interpolation with two variables speed up the numerical evaluation of the Hankel transforms in the tensor Green’s function. The results of this integral equation method for isotropic media are checked by direct comparisons with results by other workers. The results for anisotropic media are indirectly verified, mainly by checking the tensor Green’s function. The calculated results show that the effects of anisotropy on apparent resistivity and percent frequency effect are to reduce the size of the anomalies, shift the anomaly region downward toward the lower centers of the pseudosections, and enhance the effect of overburden; in other words, to shade the target from detection. This is due to the increase of currents flowing horizontally through the earth over the target. The effects of anisotropy on horizontal‐loop EM responses are to reduce the amplitude and lower the critical frequency of the maximum of the quadrature component.

scholarly journals Coronal influence on dynamos

2013 ◽  
Vol 9 (S302) ◽  
pp. 134-137 ◽  
Author(s):  
Jörn Warnecke ◽  
Axel Brandenburg
Keyword(s):  
Reynolds Number ◽  
Convection Zone ◽  
Magnetic Energy ◽  
Lower Layer ◽  
Solar Radius ◽  
Magnetic Reynolds Number ◽  
Layer Model ◽  
Dynamo Action ◽  
Turbulent Dynamo ◽  
Two Layer Model

AbstractWe report on turbulent dynamo simulations in a spherical wedge with an outer coronal layer. We apply a two-layer model where the lower layer represents the convection zone and the upper layer the solar corona. This setup is used to study the coronal influence on the dynamo action beneath the surface. Increasing the radial coronal extent gradually to three times the solar radius and changing the magnetic Reynolds number, we find that dynamo action benefits from the additional coronal extent in terms of higher magnetic energy in the saturated stage. The flux of magnetic helicity can play an important role in this context.

scholarly journals Examining cerebral hemodynamics in a two-layer model of the human head using broadband near-infrared spectroscopy

2021 ◽  
Author(s):  
Olivia Pucci
Keyword(s):  
Optical Properties ◽  
Near Infrared ◽  
Continuous Wave ◽  
Lower Layer ◽  
Homogeneous Medium ◽  
Human Head ◽  
Cerebral Hemodynamics ◽  
Layer Model ◽  
Adult Human ◽  
Two Layer Model

The development of a continuous-wave method is presented, to quantify accurately the optical properties of a two-layer model of the human head using a broadband spectral approach. In particular, focus is put on the reconstruction of the absolute absorption and scattering properties of a two-layered phantom model of the human head with steady-state multi-distance measurements by performing differential fit analysis of the near-infrared (NIR) reflectance spectrum between 700 nm and 1000 nm. The two-layer model approximation was fitted to experimental broadband absorbance measurements obtained from two-layered phantoms with known optical properties. Results demonstrated that the suggested method was able to determine the optical properties of the lower layer with minimal error at specific source-detector distances. Preliminary results on the non-invasive measurement of the optical properties of the adult human brain in a two-layer approximation are presented. Finally, a mobile wireless NIR device is used to measure changes in the temporal characteristics of cerebral hemodynamic responses to functional brain activity, in particulaur the effect of smoking. Results suggest that assuming homogeneous medium for the adult human head severely underestimates the changes in cerebral hemodynamics. Hence, it is important to take surrounding layers into consideration when performing cerebral measurements using NIR spectroscopy.

Coupling, masking and detection for induced polarization surveys in areas where low resistivity surface layers occur

1972 ◽  
Vol 3 (4) ◽  
pp. 1 ◽  
Author(s):  
J.G. Baird
Keyword(s):  
Western Australia ◽  
Electromagnetic Coupling ◽  
Induced Polarization ◽  
Electrode Configuration ◽  
Special Consideration ◽  
Signal Attenuation ◽  
Surface Layers ◽  
Sulphide Mineralization ◽  
Low Resistivity

Detection of sulphide mineralization by Induced Polarization in many areas of Western Australia is restricted by thick, low resistivity, weathered zones. Signal attenuation due to electromagnetic coupling and masking requires special consideration in design of electrode configuration. Two field examples are discussed.

Coherent structures of nonlinear barotropic-baroclinic interaction in unequal depth two-layer model

2021 ◽  
Vol 408 ◽  
pp. 126347
Author(s):  
Jiaqi Zhang ◽  
Ruigang Zhang ◽  
Liangui Yang ◽  
Quansheng Liu ◽  
Liguo Chen
Keyword(s):  
Coherent Structures ◽  
Layer Model ◽  
Two Layer Model
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