Use of the analytic signal to identify magnetic anomalies due to kimberlite pipes

Geophysics ◽  
2004 ◽  
Vol 69 (1) ◽  
pp. 180-190 ◽  
Author(s):  
Pierre Keating ◽  
Pascal Sailhac
Keyword(s):  
Magnetic Field ◽  
Target Selection ◽  
Vertical Cylinder ◽  
Analytic Signal ◽  
Moving Window ◽  
Field Orientation ◽  
Magnetic Latitude ◽  
Magnetic Signature ◽  
The Magnetic Field ◽  
Recognition Technique

The magnetic signature of most kimberlite pipes is, at high magnetic latitudes, a circular anomaly. At lower magnetic latitudes, it becomes asymmetric; and at the magnetic equator, the anomaly is mostly negative. The shape of the anomaly is also influenced by the presence of remanent magnetization. For a vertical cylinder, the shape of the analytic signal of the magnetic field is nearly independent of field orientation and remanence and always results in a compact, almost circular anomaly. A simple pattern recognition technique, based on a first‐order regression over a moving window, between the analytic signal of the observed magnetic field and the theoretical analytic signal of a magnetic vertical cylinder is an effective tool to identify potential targets. Results where the correlation coefficient between the analytic signal and the theoretical analytic signal within a moving window are above a certain threshold are retained, and additional criteria can later be used to refine the target selection. The method's practical utility is demonstrated by applying it to three different sites. The first is a well‐documented area located at high magnetic latitude (Ontario, Canada), the second is at low magnetic latitude (West Africa), and the last one is an area where many pipes have a negative magnetization (Lac de Gras, Canada).

Effect of a static magnetic field onEscherichia coliadhesion and orientation

2016 ◽  
Vol 62 (11) ◽  
pp. 944-952 ◽  
Author(s):  
Lotfi Mhamdi ◽  
Nejib Mhamdi ◽  
Naceur Mhamdi ◽  
Philippe Lejeune ◽  
Nicole Jaffrezic ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Tin Oxide ◽  
Indium Tin Oxide ◽  
Bacterial Adhesion ◽  
Parallel Magnetic Field ◽  
Field Orientation ◽  
Static Magnetic Fields ◽  
Preliminary Study ◽  
The Difference ◽  
The Magnetic Field

This preliminary study focused on the effect of exposure to 0.5 T static magnetic fields on Escherichia coli adhesion and orientation. We investigated the difference in bacterial adhesion on the surface of glass and indium tin oxide-coated glass when exposed to a magnetic field either perpendicular or parallel to the adhesion surface (vectors of magnetic induction are perpendicular or parallel to the adhesion surface, respectively). Control cultures were simultaneously grown under identical conditions but without exposure to the magnetic field. We observed a decrease in cell adhesion after exposure to the magnetic field. Orientation of bacteria cells was affected after exposure to a parallel magnetic field. On the other hand, no effect on the orientation of bacteria cells was observed after exposure to a perpendicular magnetic field.

scholarly journals Simulation study of the plasma-brake effect

2014 ◽  
Vol 32 (10) ◽  
pp. 1207-1216 ◽  
Author(s):  
P. Janhunen
Keyword(s):  
Magnetic Field ◽  
High Performance ◽  
Ionospheric Plasma ◽  
Low Earth Orbit ◽  
Earth Orbit ◽  
Breaking Force ◽  
Field Orientation ◽  
Particle In Cell ◽  
Leo Satellite ◽  
The Magnetic Field

Abstract. Plasma brake is a thin, negatively biased tether that has been proposed as an efficient concept for deorbiting satellites and debris objects from low Earth orbit. We simulate the interaction with the ionospheric plasma ram flow with the plasma-brake tether by a high-performance electrostatic particle in cell code to evaluate the thrust. The tether is assumed to be perpendicular to the flow. We perform runs for different tether voltage, magnetic-field orientation and plasma-ion mass. We show that a simple analytical thrust formula reproduces most of the simulation results well. The interaction with the tether and the plasma flow is laminar (i.e. smooth and not turbulent) when the magnetic field is perpendicular to the tether and the flow. If the magnetic field is parallel to the tether, the behaviour is unstable and thrust is reduced by a modest factor. The case in which the magnetic field is aligned with the flow can also be unstable, but does not result in notable thrust reduction. We also correct an error in an earlier reference. According to the simulations, the predicted thrust of the plasma brake is large enough to make the method promising for low-Earth-orbit (LEO) satellite deorbiting. As a numerical example, we estimate that a 5 km long plasma-brake tether weighing 0.055 kg could produce 0.43 mN breaking force, which is enough to reduce the orbital altitude of a 260 kg object mass by 100 km over 1 year.

scholarly journals Magnetic clouds' structure in the magnetosheath as observed by Cluster and Geotail: four case studies

2014 ◽  
Vol 32 (10) ◽  
pp. 1247-1261 ◽  
Author(s):  
L. Turc ◽  
D. Fontaine ◽  
P. Savoini ◽  
E. K. J. Kilpua
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Magnetic Fields ◽  
Bow Shock ◽  
Field Direction ◽  
Magnetic Clouds ◽  
Magnetic Field Direction ◽  
Field Orientation ◽  
The Impact ◽  
The Magnetic Field

Abstract. Magnetic clouds (MCs) are large-scale magnetic flux ropes ejected from the Sun into the interplanetary space. They play a central role in solar–terrestrial relations as they can efficiently drive magnetic activity in the near-Earth environment. Their impact on the Earth's magnetosphere is often attributed to the presence of southward magnetic fields inside the MC, as observed in the upstream solar wind. However, when they arrive in the vicinity of the Earth, MCs first encounter the bow shock, which is expected to modify their properties, including their magnetic field strength and direction. If these changes are significant, they can in turn affect the interaction of the MC with the magnetosphere. In this paper, we use data from the Cluster and Geotail spacecraft inside the magnetosheath and from the Advanced Composition Explorer (ACE) upstream of the Earth's environment to investigate the impact of the bow shock's crossing on the magnetic structure of MCs. Through four example MCs, we show that the evolution of the MC's structure from the solar wind to the magnetosheath differs largely from one event to another. The smooth rotation of the MC can either be preserved inside the magnetosheath, be modified, i.e. the magnetic field still rotates slowly but at different angles, or even disappear. The alteration of the magnetic field orientation across the bow shock can vary with time during the MC's passage and with the location inside the magnetosheath. We examine the conditions encountered at the bow shock from direct observations, when Cluster or Geotail cross it, or indirectly by applying a magnetosheath model. We obtain a good agreement between the observed and modelled magnetic field direction and shock configuration, which varies from quasi-perpendicular to quasi-parallel in our study. We find that the variations in the angle between the magnetic fields in the solar wind and in the magnetosheath are anti-correlated with the variations in the shock obliquity. When the shock is in a quasi-parallel regime, the magnetic field direction varies significantly from the solar wind to the magnetosheath. In such cases, the magnetic field reaching the magnetopause cannot be approximated by the upstream magnetic field. Therefore, it is important to take into account the conditions at the bow shock when estimating the impact of an MC with the Earth's environment because these conditions are crucial in determining the magnetosheath magnetic field, which then interacts with the magnetosphere.

On the absence of plasma wave emissions and the magnetic field orientation in the distant magnetosheath

1994 ◽  
Vol 21 (24) ◽  
pp. 2761-2764 ◽  
Author(s):  
F. V. Coroniti ◽  
E. W. Greenstadt ◽  
S. L. Moses ◽  
B. T. Tsurutani ◽  
E. J. Smith
Keyword(s):  
Magnetic Field ◽  
Plasma Wave ◽  
Field Orientation ◽  
Magnetic Field Orientation ◽  
The Magnetic Field

scholarly journals The Magnetic Field of the Crab as Revealed by New, High Resolution, Multi-Band Radio Images

1990 ◽  
Vol 140 ◽  
pp. 79-80
Author(s):  
M. F. Bietenholz ◽  
P. P. Kronberg
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Crab Nebula ◽  
Radio Observations ◽  
Field Orientation ◽  
Magnetic Field Orientation ◽  
The Crab Nebula ◽  
The Magnetic Field ◽  
Made In ◽  
Multi Band

We present and describe recent radio observations of the Crab Nebula, which allow us to determine the magnetic field orientation and depolarization at unprecedented resolution. The observations were made in 1987-1988 using all four configurations of the VLA, at 1410,1515,4625, and 4885 MHz. The resulting maps were all convolved with a clean beam of 1.8″ × 2.0″, elongated in P.A. 80°, and the residuals added back in.

scholarly journals The geometry of the magnetic field in the central molecular zone measured by PILOT

2019 ◽  
Vol 630 ◽  
pp. A74 ◽  
Author(s):  
A. Mangilli ◽  
J. Aumont ◽  
J.-Ph. Bernard ◽  
A. Buzzelli ◽  
G. de Gasperis ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Molecular Clouds ◽  
Angular Resolution ◽  
Galactic Center ◽  
Galactic Plane ◽  
Mean Field ◽  
Field Orientation ◽  
Center Region ◽  
The Mean ◽  
The Magnetic Field

We present the first far infrared (FIR) dust emission polarization map covering the full extent of Milky Way’s central molecular zone (CMZ). The data, obtained with the PILOT balloon-borne experiment, covers the Galactic center region − 2° < ℓ < 2°, − 4° < b < 3° at a wavelength of 240 μm and an angular resolution of 2.2′. From our measured dust polarization angles, we infer a magnetic field orientation projected onto the plane of the sky (POS) that is remarkably ordered over the full extent of the CMZ, with an average tilt angle of ≃22° clockwise with respect to the Galactic plane. Our results confirm previous claims that the field traced by dust polarized emission is oriented nearly orthogonally to the field traced by GHz radio synchrotron emission in the Galactic center region. The observed field structure is globally compatible with the latest Planck polarization data at 353 and 217 GHz. Upon subtraction of the extended emission in our data, the mean field orientation that we obtain shows good agreement with the mean field orientation measured at higher angular resolution by the JCMT within the 20 and 50 km s−1 molecular clouds. We find no evidence that the magnetic field orientation is related to the 100 pc twisted ring structure within the CMZ. The low polarization fraction in the Galactic center region measured with Planck at 353 GHz combined with a highly ordered projected field orientation is unusual. This feature actually extends to the whole inner Galactic plane. We propose that it could be caused by the increased number of turbulent cells for the long lines of sight towards the inner Galactic plane or to dust properties specific to the inner regions of the Galaxy. Assuming equipartition between magnetic pressure and ram pressure, we obtain magnetic field strength estimates of the order of 1 mG for several CMZ molecular clouds.

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