Transformation of VLF data into apparent resistivities and phases

Geophysics ◽  
1999 ◽  
Vol 64 (5) ◽  
pp. 1393-1402 ◽  
Author(s):  
Mehran Gharibi ◽  
Laust B. Pedersen
Keyword(s):  
Magnetic Field ◽  
Electrical Conductivity ◽  
Large Scale ◽  
Low Cost ◽  
Real Data ◽  
Geological Structure ◽  
Direct Estimate ◽  
Horizontal Magnetic Field ◽  
Near Surface ◽  
Full Solution

In the VLF method, the ratio between the vertical and the horizontal magnetic field or the total magnetic field anomaly is measured to detect localized changes in electrical conductivity contrasts. Although the VLF technique has probably been the most popular electromagnetic (EM) tool for mapping near‐surface geological structures in a large scale for the past few decades because of the low cost and speed with which surveys can be carried out, the measurements themselves do not give a direct estimate of electrical conductivity. A fast iterative method has been developed to estimate the impedance or apparent resistivity and phases from measurements of the magnetic components at the surface of a 2-D geological structure. From Maxwell’s equations in E-polarization, a relation was derived between the horizontal and vertical components of the magnetic field. A full solution has been obtained by making use of the fact that the secondary horizontal and vertical magnetic fields are of internal origin and form a Hilbert transform pair. Synthetic and real VLF data have been used to evaluate the performance and limitation of the method. Using synthetic and real data, one can achieve a full recovery of the E-polarization impedance as long as the length of the profile is sufficiently long. A number of precautions must be taken to ensure reliable estimation of impedance results.

scholarly journals Experimental Methods for Investigation of Drilling Fluid Displacement in Irregular Annuli

Energies ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 5201
Author(s):  
Bjørnar Lund ◽  
Ali Taghipour ◽  
Jan David Ytrehus ◽  
Arild Saasen
Keyword(s):  
Electrical Conductivity ◽  
Large Scale ◽  
Drilling Fluid ◽  
Low Cost ◽  
Relevant Information ◽  
Experimental Methods ◽  
Optical Measurements ◽  
Complex Flow ◽  
Large Scale Systems ◽  
Fluid Displacement

Experimental methods are still indispensable for fluid mechanics research, despite advancements in the modelling and computer simulation field. Experimental data are vital for validating simulations of complex flow systems. However, measuring the flow in industrially relevant systems can be difficult for several reasons. Here we address flow measurement challenges related to cementing of oil wells, where main experimental issues are related to opacity of the fluids and the sheer size of the system. The main objective is to track the propagation of a fluid-fluid interface during a two-fluid displacement process, and thereby to characterize the efficiency of the displacement process. We describe the implementation and use of an array of electrical conductivity probes, and demonstrate with examples how the signals can be used to recover relevant information about the displacement process. To our knowledge this is the most extensive use of this measurement method for studying displacement in a large-scale laboratory setup. Optical measurements and visual observations are challenging and/or costly in such large-scale systems, but can still provide qualitative information as shown in this article. Using electrical conductivity probes is a robust and fairly low-cost experimental method for characterizing fluid-fluid displacement in large-scale systems.

scholarly journals Large-scale dynamos in rapidly rotating plane layer convection

2018 ◽  
Vol 612 ◽  
pp. A97 ◽  
Author(s):  
P. J. Bushby ◽  
P. J. Käpylä ◽  
Y. Masada ◽  
A. Brandenburg ◽  
B. Favier ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Plane Layer ◽  
Cycle Period ◽  
Dynamo Action ◽  
Horizontal Magnetic Field ◽  
Vortex Instability ◽  
Large Scale Vortex ◽  
The Mean ◽  
The Magnetic Field

Context.Convectively driven flows play a crucial role in the dynamo processes that are responsible for producing magnetic activity in stars and planets. It is still not fully understood why many astrophysical magnetic fields have a significant large-scale component.Aims.Our aim is to investigate the dynamo properties of compressible convection in a rapidly rotating Cartesian domain, focusing upon a parameter regime in which the underlying hydrodynamic flow is known to be unstable to a large-scale vortex instability.Methods.The governing equations of three-dimensional non-linear magnetohydrodynamics (MHD) are solved numerically. Different numerical schemes are compared and we propose a possible benchmark case for other similar codes.Results.In keeping with previous related studies, we find that convection in this parameter regime can drive a large-scale dynamo. The components of the mean horizontal magnetic field oscillate, leading to a continuous overall rotation of the mean field. Whilst the large-scale vortex instability dominates the early evolution of the system, the large-scale vortex is suppressed by the magnetic field and makes a negligible contribution to the mean electromotive force that is responsible for driving the large-scale dynamo. The cycle period of the dynamo is comparable to the ohmic decay time, with longer cycles for dynamos in convective systems that are closer to onset. In these particular simulations, large-scale dynamo action is found only when vertical magnetic field boundary conditions are adopted at the upper and lower boundaries. Strongly modulated large-scale dynamos are found at higher Rayleigh numbers, with periods of reduced activity (grand minima-like events) occurring during transient phases in which the large-scale vortex temporarily re-establishes itself, before being suppressed again by the magnetic field.

scholarly journals Near-surface stellar magneto-convection: simulations for the Sun and a metal-poor solar analog

2008 ◽  
Vol 4 (S259) ◽  
pp. 233-234
Author(s):  
Matthias Steffen ◽  
H.-G. Ludwig ◽  
O. Steiner
Keyword(s):  
Magnetic Field ◽  
Preliminary Analysis ◽  
Field Component ◽  
Stellar Atmospheres ◽  
Thin Layers ◽  
The Sun ◽  
Horizontal Magnetic Field ◽  
Near Surface ◽  
Hydrodynamical Models ◽  
Metal Abundances

AbstractWe present 2D local box simulations of near-surface radiative magneto-convection with prescribed magnetic flux, carried out with the MHD version of the CO5BOLD code for the Sun and a solar-like star with a metal-poor chemical composition (metal abundances reduced by a factor 100, [M/H] = −2). The resulting magneto-hydrodynamical models can be used to study the influence of the metallicity on the properties of magnetized stellar atmospheres. A preliminary analysis indicates that the horizontal magnetic field component tends to be significantly stronger in the optically thin layers of metal-poor stellar atmospheres.

scholarly journals Cellular Network Infrastructure: The Future of Fog Monitoring?

2015 ◽  
Vol 96 (10) ◽  
pp. 1687-1698 ◽  
Author(s):  
Noam David ◽  
Omry Sendik ◽  
Hagit Messer ◽  
Pinhas Alpert
Keyword(s):  
Communication Networks ◽  
Low Cost ◽  
Real Data ◽  
Near Surface ◽  
Theoretical Simulation ◽  
High Data ◽  
Data Rates ◽  
Crucial Information ◽  
Current Monitoring ◽  
Commercial Microwave Links

Abstract Severe visibility limitations resulting from fog may lead to acute transportation accidents and high losses of property and lives. Thus, reliable monitoring facilities are of extreme importance. Nevertheless, current monitoring instruments suffer from low spatial resolution, high costs, or lack of precision at near-surface levels. It has, however, recently been shown that the commercial microwave links that form the infrastructure of cellular communication networks can provide crucial information regarding the appearance of dense fog and its intensity. Typical microwave systems currently in operation make use of frequencies between 6 and 40 GHz and, thus, can only monitor heavy fog. However, there is a growing demand for high data rates and expanded bandwidth in modern mobile radio networks. As a result, higher frequencies (e.g., around 80 GHz) are being implemented in order to fulfill these increased requirements. Notably, the attenuation induced as a result of fog at a given intensity increases as operating frequency rises, allowing, for the first time, the possibility of using this system to monitor typical fog intensities, at high resolution and low cost. Here, a theoretical simulation is presented in which simulated fog patches are introduced into an area where a network of links is deployed. Two-dimensional maps are generated utilizing the simulated microwave network to represent sensitivity thresholds for fog detection at three different frequencies: 20, 38, and 80 GHz. Real-data measurements of fog are also demonstrated using 38-GHz band links. The results indicate the vast future potential of commercial microwave links as an opportunistic system for monitoring fog.

2-Dimensional soil and vadose-zone representation using an EM38 and EM34 and a laterally constrained inversion model

Soil Research ◽  
2009 ◽  
Vol 47 (8) ◽  
pp. 809 ◽  
Author(s):  
J. Triantafilis ◽  
F. A. Monteiro Santos
Keyword(s):  
Electrical Conductivity ◽  
Vadose Zone ◽  
Root Zone ◽  
Clay Content ◽  
Inversion Algorithm ◽  
Near Surface ◽  
Particle Size Fractions ◽  
Murray Darling Basin ◽  
Full Solution ◽  
Soil Particle Size Fractions

The network of prior streams and palaeochannels common across the Riverine Plains of the Murray–Darling Basin act as conduits for the redistribution of water and soluble salts beneath the root-zone. To improve scientific understanding of these hydrological processes there is the need to better represent and map the connectivity and spatial extent of these physiographic and stratigraphic features. Groundbased electromagnetic (EM) instruments, which measure bulk soil electrical conductivity (σa), have been used widely to map their areal distribution across the landscape. However, methods to resolve their location with depth have rarely been attempted. In this paper we employ a 1-D inversion algorithm with 2-D smoothness constraints to predict the true electrical conductivity (σ) at discrete depth increments using EM data. The EM data we use include the root-zone measuring EM38 and the deeper sensing EM34. We collected EM38 data in the vertical (EM38v) and horizontal (EM38h) dipole modes and EM34 data in the horizontal mode and coil spacing of 10, 20, and 40 m (respectively, EM34-10, EM34-20, and EM34-40). In order to compare and contrast the value of the various EM data we carried out multiple inversions using different combinations, which include: independent inversions of (i) EM38 (root-zone) and (ii) EM34 data (vadose-zone), and in combination using (iii) EM38v, EM38h, and EM34-10 (near-surface), and (iv) all 5 EM datasets (regolith) available. The general patterns of σ are shown to compare favourably with the known pedoderms, physiographic, and stratigraphic features and soil particle size fractions collected from calibration cores drilled across the lower Macquarie Valley study area. In general we find that the EM38 assists in resolving root-zone variability, specifically duplex soil profiles and physiographic features such as prior streams, while the use of the EM34 assists in resolving the stratigraphic nature of the vadose-zone and specifically the likely location of palaeochannels and subsurface anomalies that may indicate the location of good quality groundwater and/or clay aquitards. In this case, our potential to use σ to predict clay content is limited by the non-linearity of the cumulative functions. In order to improve on the non-linearity of our inversion we need to develop a full solution of the forward problem.

scholarly journals Edge-Based Missing Data Imputation in Large-Scale Environments

Information ◽  
2021 ◽  
Vol 12 (5) ◽  
pp. 195
Author(s):  
Davide Andrea Guastella ◽  
Guilhem Marcillaud ◽  
Cesare Valenti
Keyword(s):  
Urban Environment ◽  
Large Scale ◽  
Smart Cities ◽  
Low Cost ◽  
Real Data ◽  
Missing Data Imputation ◽  
Large Scale Data ◽  
Iot Devices ◽  
Edge Based ◽  
The One

Smart cities leverage large amounts of data acquired in the urban environment in the context of decision support tools. These tools enable monitoring the environment to improve the quality of services offered to citizens. The increasing diffusion of personal Internet of things devices capable of sensing the physical environment allows for low-cost solutions to acquire a large amount of information within the urban environment. On the one hand, the use of mobile and intermittent sensors implies new scenarios of large-scale data analysis; on the other hand, it involves different challenges such as intermittent sensors and integrity of acquired data. To this effect, edge computing emerges as a methodology to distribute computation among different IoT devices to analyze data locally. We present here a new methodology for imputing environmental information during the acquisition step, due to missing or otherwise out of order sensors, by distributing the computation among a variety of fixed and mobile devices. Numerous experiments have been carried out on real data to confirm the validity of the proposed method.

Graphene/graphene nanoplatelets reinforced polyamide nanocomposites: A review

2021 ◽  
pp. 095400832110112
Author(s):  
Himanshu V Madhad ◽  
Nikita S Mishra ◽  
Sunil B Patel ◽  
Siddhi S Panchal ◽  
Rusvi A Gandhi ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
3D Printing ◽  
Aspect Ratio ◽  
Large Scale ◽  
Low Cost ◽  
Academic Research ◽  
Graphene Nanoplatelets ◽  
High Electrical Conductivity ◽  
Multifunctional Nanocomposites ◽  
Preparation Techniques

Graphene and its derivatives have received considerable attention in industrial and academic research due to their unique, useful properties and applications. The use of graphene is still difficult due to its high cost of production. Hence, graphene nanoplatelets (GNPs) have been identified as a substitute for graphene, which are produced in large scale at a very low cost. Moreover, GNPs have played a significant role in various engineering thermoplastic materials [i.e., polyamides (PAs)] to enhance their properties and applications. The GNPs help in the production of low-cost multifunctional nanocomposites with notable useful properties such as high electrical conductivity, mechanical strength, and high aspect ratio. The GNPs based nanocomposites have a broad spectrum of application areas including 3D-printing, automotive materials, electrical appliances, low-cost composites films, and many more. This review summarizes different preparation techniques, properties, and applications of GNPs based PAs nanocomposites as reported in current literature.

Evaluation of a rapid hybrid spectral-spatial domain 3D forward-modeling approach for loop-loop electromagnetic induction quadrature data acquired in low-induction-number environments

Geophysics ◽  
2016 ◽  
Vol 81 (6) ◽  
pp. E447-E458 ◽  
Author(s):  
Julien Guillemoteau ◽  
Jens Tronicke
Keyword(s):  
Electrical Conductivity ◽  
Large Scale ◽  
Structural Information ◽  
Forward Modeling ◽  
Spatial Domain ◽  
Near Surface ◽  
Homogeneous Half Space ◽  
Subsurface Environments ◽  
Em Induction ◽  
The Right

When exploring subsurface environments using electromagnetic (EM) induction (EMI) tools, approximate forward-modeling methods based on a homogeneous half-space kernel have been extensively evaluated in the past. For large-scale exploration methods, such as magnetotellurics, marine EM, airborne EM, transient EM, and large offset loop-loop harmonic EM, such forward-modeling approaches are limited because the kernel depends strongly on the subsurface distribution of electrical conductivity. However, the response of small portable EMI loop-loop sensors applied in a low-induction number (LIN) context are known to be more linearly related to the true distribution of electrical conductivity. Thus, data collected using such sensors are more adapted to an approximate forward-modeling with a conductivity-independent kernel. We have evaluated the bias of such an approximate modeling for the case of portable multiconfiguration system measurements in 1D, 2D, and 3D contexts. Our result shows that the approximate approach tends to underestimate the conductivity of more conductive targets but is able to reproduce the right structural information. Compared with previous algorithms presented in the literature, we solved the approximate forward-modeling problem in the hybrid spectral-spatial domain to speed up the computation. Considering the level of accuracy in structural modeling as well as the computational efficiency of our hybrid spectral-spatial approach, we conclude that this method is especially suitable for near-surface, large-scale mapping applications in LIN environments as typically encountered in soil sciences and archaeological studies. For such applications, our approach can be implemented in rapid multichannel deconvolution procedures.

Mixed convection in a horizontal duct with bottom heating and strong transverse magnetic field

2014 ◽  
Vol 757 ◽  
pp. 33-56 ◽  
Author(s):  
Xuan Zhang ◽  
Oleg Zikanov
Keyword(s):  
Magnetic Field ◽  
Mixed Convection ◽  
Large Scale ◽  
Three Dimensional ◽  
Transverse Magnetic ◽  
Temperature Fields ◽  
Horizontal Magnetic Field ◽  
Bottom Heating ◽  
Field Lines ◽  
The Magnetic Field

AbstractMixed convection in a horizontal duct with imposed transverse horizontal magnetic field is studied using direct numerical simulations (DNS) and linear stability analysis. The duct’s walls are electrically insulated and thermally insulated with the exception of the bottom wall, at which constant-rate heating is applied. The focus of the study is on flows at high Hartmann ($\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}\mathit{Ha}\le 800$) and Grashof ($\mathit{Gr}\le 10^9$) numbers. It is found that, while conventional turbulence is fully suppressed, the natural convection mechanism leads to the development of large-scale coherent structures. Two types of flows are found. One is the ‘low-$\mathit{Gr}$’ regime, in which the structures are rolls aligned with the magnetic field and velocity and temperature fields are nearly uniform along the magnetic field lines outside of the boundary layers. Another is the ‘high-$\mathit{Gr}$’ regime, in which the convection appears as a combination of similar rolls oriented along the magnetic field lines and streamwise-oriented rolls. In this case, velocity and temperature distributions are anisotropic, but three-dimensional.

scholarly journals Simulating the Coronal Evolution of Bipolar Active Regions to Investigate the Formation of Flux Ropes

Solar Physics ◽  
2021 ◽  
Vol 296 (1) ◽  
Author(s):  
S. L. Yardley ◽  
D. H. Mackay ◽  
L. M. Green
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Initial Conditions ◽  
Free Field ◽  
Active Regions ◽  
Coronal Magnetic Field ◽  
Solar Dynamics Observatory ◽  
Horizontal Magnetic Field ◽  
Nonlinear Force ◽  
Force Free Field

AbstractThe coronal magnetic field evolution of 20 bipolar active regions (ARs) is simulated from their emergence to decay using the time-dependent nonlinear force-free field method of Mackay, Green, and van Ballegooijen (Astrophys. J. 729, 97, 2011). A time sequence of cleaned photospheric line-of-sight magnetograms, which covers the entire evolution of each AR, is used to drive the simulation. A comparison of the simulated coronal magnetic field with the 171 and 193 Å observations obtained by the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA), is made for each AR by manual inspection. The results show that it is possible to reproduce the evolution of the main coronal features such as small- and large-scale coronal loops, filaments and sheared structures for 80% of the ARs. Varying the boundary and initial conditions, along with the addition of physical effects such as Ohmic diffusion, hyperdiffusion and a horizontal magnetic field injection at the photosphere, improves the match between the observations and simulated coronal evolution by 20%. The simulations were able to reproduce the build-up to eruption for 50% of the observed eruptions associated with the ARs. The mean unsigned time difference between the eruptions occurring in the observations compared to the time of eruption onset in the simulations was found to be ≈5 hrs. The simulations were particularly successful in capturing the build-up to eruption for all four eruptions that originated from the internal polarity inversion line of the ARs. The technique was less successful in reproducing the onset of eruptions that originated from the periphery of ARs and large-scale coronal structures. For these cases global, rather than local, nonlinear force-free field models must be used. While the technique has shown some success, eruptions that occur in quick succession are difficult to reproduce by this method and future iterations of the model need to address this.

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