Magnetic Fields in AGN

AbstractWe review VLBI polarization results. In particular, we discuss the a) “shock in jet paradigm”, b) the orientation of the magnetic field in jets as a function of optical identification, c) rotation measure and Faraday dispersion measurements as a probe of the narrow line region, and d) future directions of polarization observations. Results we emphasize are i) there is still a strong correlation between optical L/C ratio or EW and magnetic field orientation in the jets of blazars, even for high redshift weak-lined objects, ii) observed rotation measures are much smaller than expected from the properties of the NLR, except for some CSS sources. Also iii) a faint boundary layer or sheath (with a parallel magnetic field) has been observed around the jet of the weak-lined blazar 1055+018, and iv) circular polarization has been detected for the first time in the jets of 3C 84 and 3C 279.

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Effect of a static magnetic field onEscherichia coliadhesion and orientation

Canadian Journal of Microbiology ◽

10.1139/cjm-2015-0839 ◽

2016 ◽

Vol 62 (11) ◽

pp. 944-952 ◽

Cited By ~ 1

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.

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Connecting magnetic fields from sub-galactic scale to clusters of galaxies and beyond with cosmological MHD simulations

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316006396 ◽

2015 ◽

Vol 11 (A29B) ◽

pp. 699-699

Author(s):

Klaus Dolag ◽

Alexander M. Beck ◽

Alexander Arth

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Heat Transport ◽

Galaxy Clusters ◽

Large Scale ◽

High Redshift ◽

Galactic Halos ◽

Rotation Measure ◽

The Magnetic Field ◽

Good Agreement

AbstractUsing the MHD version of Gadget3 (Stasyszyn, Dolag & Beck 2013) and a model for the seeding of magnetic fields by supernovae (SN), we performed simulations of the evolution of the magnetic fields in galaxy clusters and study their effects on the heat transport within the intra cluster medium (ICM). This mechanism – where SN explosions during the assembly of galaxies provide magnetic seed fields – has been shown to reproduce the magnetic field in Milky Way-like galactic halos (Beck et al. 2013). The build up of the magnetic field at redshifts before z = 5 and the accordingly predicted rotation measure evolution are also in good agreement with current observations. Such magnetic fields present at high redshift are then transported out of the forming protogalaxies into the large-scale structure and pollute the ICM (in a similar fashion to metals transport). Here, complex velocity patterns, driven by the formation process of cosmic structures are further amplifying and distributing the magnetic fields. In galaxy clusters, the magnetic fields therefore get amplified to the observed μG level and produce the observed amplitude of rotation measures of several hundreds of rad/m2. We also demonstrate that heat conduction in such turbulent fields on average is equivalent to a suppression factor around 1/20th of the classical Spitzer value and in contrast to classical, isotropic heat transport leads to temperature structures within the ICM compatible with observations (Arth et al. 2014).

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The effect of magnetic field on the dynamics of gas bubbles in water electrolysis

Scientific Reports ◽

10.1038/s41598-021-87947-9 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Yan-Hom Li ◽

Yen-Ju Chen

Keyword(s):

Magnetic Field ◽

Swirling Flow ◽

Gas Bubbles ◽

Water Electrolysis ◽

Platinum Electrodes ◽

Optimal Layout ◽

Parallel Magnetic Field ◽

Hydrogen Bubbles ◽

The Magnetic Field ◽

Sluggish Flow

AbstractThis study determines the effect of the configuration of the magnetic field on the movement of gas bubbles that evolve from platinum electrodes. Oxygen and hydrogen bubbles respectively evolve from the surface of the anode and cathode and behave differently in the presence of a magnetic field due to their paramagnetic and diamagnetic characteristics. A magnetic field perpendicular to the surface of the horizontal electrode causes the bubbles to revolve. Oxygen and hydrogen bubbles revolve in opposite directions to create a swirling flow and spread the bubbles between the electrodes, which increases conductivity and the effectiveness of electrolysis. For vertical electrodes under the influence of a parallel magnetic field, a horizontal Lorentz force effectively detaches the bubbles and increases the conductivity and the effectiveness of electrolysis. However, if the layout of the electrodes and magnetic field results in upward or downward Lorentz forces that counter the buoyancy force, a sluggish flow in the duct inhibits the movement of the bubbles and decreases the conductivity and the charging performance. The results in this study determine the optimal layout for an electrode and a magnetic field to increase the conductivity and the effectiveness of water electrolysis, which is applicable to various fields including energy conversion, biotechnology, and magnetohydrodynamic thruster used in seawater.

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MHD flows in a U-channel under the influence of the spatially different channel-wall electric conductivity and of the magnetic field orientation

Journal of Mechanical Science and Technology ◽

10.1007/s12206-021-0918-0 ◽

2021 ◽

Author(s):

Yang Luo ◽

Xiaowen Fan ◽

Chang Nyung Kim

Keyword(s):

Magnetic Field ◽

Electric Conductivity ◽

Channel Wall ◽

Field Orientation ◽

Mhd Flows ◽

Magnetic Field Orientation ◽

The Magnetic Field

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Simulation study of the plasma-brake effect

Annales Geophysicae ◽

10.5194/angeo-32-1207-2014 ◽

2014 ◽

Vol 32 (10) ◽

pp. 1207-1216 ◽

Cited By ~ 12

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.

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Principal Component Gradiometer technique for removal of spacecraft-generated disturbances from magnetic field data

10.5194/gi-2020-10 ◽

2020 ◽

Cited By ~ 1

Author(s):

Ovidiu Dragoş Constantinescu ◽

Hans-Ulrich Auster ◽

Magda Delva ◽

Olaf Hillenmaier ◽

Werner Magnes ◽

...

Keyword(s):

Magnetic Field ◽

Principal Component ◽

Field Measurements ◽

Magnetic Field Data ◽

Service Oriented ◽

Sensor Configuration ◽

Time Required ◽

First Time ◽

The Magnetic Field

Abstract. In situ measurement of the magnetic field using space borne instruments requires either a magnetically clean platform and/or a very long boom for accommodating magnetometer sensors at a large distance from the spacecraft body. This significantly drives up the costs and time required to build a spacecraft. Here we present an alternative sensor configuration and an algorithm allowing for ulterior removal of the spacecraft generated disturbances from the magnetic field measurements, thus lessening the need for a magnetic cleanliness program and allowing for shorter boom length. The proposed algorithm is applied to the Service Oriented Spacecraft Magnetometer (SOSMAG) onboard the Korean geostationary satellite GeoKompsat-2A (GK2A) which uses for the first time a multi-sensor configuration for onboard data cleaning. The successful elimination of disturbances originating from several sources validates the proposed cleaning technique.

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The UVMag space project: UV and visible spectropolarimetry of massive stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314007212 ◽

2014 ◽

Vol 9 (S307) ◽

pp. 389-390

Author(s):

Coralie Neiner ◽

Keyword(s):

Magnetic Field ◽

High Resolution ◽

Massive Stars ◽

Spectral Energy Distribution ◽

Spectral Energy ◽

Medium Size ◽

Space Project ◽

First Time ◽

The Magnetic Field ◽

Circumstellar Environment

AbstractUVMag is a medium-size space telescope equipped with a high-resolution spectropolarimetrer working in the UV and visible domains. It will be proposed to ESA for a future M mission. It will allow scientists to study all types of stars as well as e.g. exoplanets and the interstellar medium. It will be particularly useful for massive stars, since their spectral energy distribution peaks in the UV. UVMag will allow us to study massive stars and their circumstellar environment (in particular the stellar wind) spectroscopically in great details. Moreover, with UVMag's polarimetric capabilities we will be able, for the first time, to measure the magnetic field of massive stars simultaneously at the stellar surface and in the wind lines, i.e. to completely map their magnetosphere.

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The upper atmospheres of Uranus and Neptune

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2019.0478 ◽

2020 ◽

Vol 378 (2187) ◽

pp. 20190478 ◽

Cited By ~ 2

Author(s):

Henrik Melin

Keyword(s):

Magnetic Field ◽

Joule Heating ◽

Critical Role ◽

Upper Atmosphere ◽

Heating Rates ◽

James Webb Space Telescope ◽

Vertical Distributions ◽

Auroral Current ◽

First Time ◽

The Magnetic Field

We review the current understanding of the upper atmospheres of Uranus and Neptune, and explore the upcoming opportunities available to study these exciting planets. The ice giants are the least understood planets in the solar system, having been only visited by a single spacecraft, in 1986 and 1989, respectively. The upper atmosphere plays a critical role in connecting the atmosphere to the forces and processes contained within the magnetic field. For example, auroral current systems can drive charged particles into the atmosphere, heating it by way of Joule heating. Ground-based observations of H 3 + provides a powerful remote diagnostic of the physical properties and processes that occur within the upper atmosphere, and a rich dataset exists for Uranus. These observations span almost three decades and have revealed that the upper atmosphere has continuously cooled between 1992 and 2018 at about 8 K/year, from approximately 750 K to approximately 500 K. The reason for this trend remain unclear, but could be related to seasonally driven changes in the Joule heating rates due to the tilted and offset magnetic field, or could be related to changing vertical distributions of hydrocarbons. H 3 + has not yet been detected at Neptune, but this discovery provides low-hanging fruit for upcoming facilities such as the James Webb Space Telescope and the next generation of 30 m telescopes. Detecting H 3 + at Neptune would enable the characterization of its upper atmosphere for the first time since 1989. To fully understand the ice giants, we need dedicated orbital missions, in the same way the Cassini spacecraft explored Saturn. Only by combining in situ observations of the magnetic field with in-orbit remote sensing can we get the complete picture of how energy moves between the atmosphere and the magnetic field. This article is part of a discussion meeting issue ‘Future exploration of ice giant systems’.

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

Annales Geophysicae ◽

10.5194/angeo-32-1247-2014 ◽

2014 ◽

Vol 32 (10) ◽

pp. 1247-1261 ◽

Cited By ~ 7

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.

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