817 research outputs found
Transmission Line Analogy for Relativistic Poynting-Flux Jets
Radio emission, polarization, and Faraday rotation maps of the radio jet of
the galaxy 3C 303 have shown that one knot of this jet carries a {\it
galactic}-scale electric current and that it is magnetically dominated. We
develop the theory of magnetically dominated or Poynting-flux jets by making an
analogy of a Poynting jet with a transmission line or waveguide carrying a net
current and having a potential drop across it (from the jet's axis to its
radius) and a definite impedance which we derive. Time-dependent but not
necessarily small perturbations of a Poynting-flux jet are described by the
"telegrapher's equations." These predict the propagation speed of disturbances
and the effective wave impedance for forward and backward propagating wave
components. A localized disturbance of a Poynting jet gives rise to localized
dissipation in the jet which may explain the enhanced synchrotron radiation in
the knots of the 3C 303 jet, and also in the apparently stationary knot HST-1
in the jet near the nucleus of the nearby galaxy M87. For a relativistic
Poynting jet on parsec scales, the reflected voltage wave from an inductive
termination or load can lead to a backward propagating wave which breaks down
the magnetic insulation of the jet giving . At the
threshold for breakdown, , positive and negative
particles are directly accelerated in the direction which is
approximately along the jet axis. Acceleration can occur up to Lorentz factors
. This particle acceleration mechanism is distinct from that in
shock waves and that in magnetic field reconnection.Comment: 8 pages, 6 figure
Wave model for longitudinal dispersion: Application to the laminar-flow tubular reactor
The wave model for longitudinal dispersion, published elsewhere as an alternative to the commonly used dispersed plug-flow model, is applied to the classic case of the laminar-flow tubular reactor. The results are compared in a wide range of situations to predictions by the dispersed plug-flow model as well as to exact numerical calculations with the 2-D model of the reactor and to other available methods. In many practical cases, the solutions of the wave model agree closely with the exact data. The wave model has a much wider region of validity than the dispersed plug-flow model, has a distinct physical background, and is easier to use for reactor calculations. This provides additional support to the theory developed elsewhere. The properties and the applicability of the wave model to situations with rapidly changing concentration fields are discussed. Constraints to be satisfied are established to use the new theory with confidence for arbitrary initial and boundary conditions
Wave Concept in the Theory of Hydrodynamical Dispersion - a Maxwellian Type Approach
A new approach to the modelling of chemical reactors and contactors is discussed. This approach argues that the dispersion should, under most circumstances, be based on Maxwell's, rather than Fick's diffusion law. As a pair of first-order partial differential equations of the hyperbolic type and requiring only inlet conditions, the wave model is more realistic physically, has a much wider range of validity and in many practical cases is simpler mathematically. Only mass transfer problems are considered, but the results apply equally well to the hydrodynamic dispersion of heat. It is explained why the standard dispersion model fails in many practical applications and why the new wave model gives much better results
Oxygen and hydrogen ion abundance in the near-Earth magnetosphere: Statistical results on the response to the geomagnetic and solar wind activity conditions
The composition of ions plays a crucial role for the fundamental plasma
properties in the terrestrial magnetosphere. We investigate the
oxygen-to-hydrogen ratio in the near-Earth magnetosphere from -10 RE<XGSE}< 10
RE. The results are based on seven years of ion flux measurements in the energy
range ~10 keV to ~955 keV from the RAPID and CIS instruments on board the
Cluster satellites. We find that (1) hydrogen ions at ~10 keV show only a
slight correlation with the geomagnetic conditions and interplanetary magnetic
field changes. They are best correlated with the solar wind dynamic pressure
and density, which is an expected effect of the magnetospheric compression; (2)
~10 keV O+ ion intensities are more strongly affected during disturbed phase of
a geomagnetic storm or substorm than >274 keV O+ ion intensities, relative to
the corresponding hydrogen intensities; (3) In contrast to ~10 keV ions, the
>274 keV O+ ions show the strongest acceleration during growth phase and not
during the expansion phase itself. This suggests a connection between the
energy input to the magnetosphere and the effective energization of energetic
ions during growth phase; (4) The ratio between quiet and disturbed times for
the intensities of ion ionospheric outflow is similar to those observed in the
near-Earth magnetosphere at >274 keV. Therefore, the increase of the energetic
ion intensity during disturbed time is more likely due to the intensification
than to the more effective acceleration of the ionospheric source. In
conclusion, the energization process in the near-Earth magnetosphere is mass
dependent and it is more effective for the heavier ions
A New Radio - X-Ray Probe of Galaxy Cluster Magnetic Fields
Results are presented of a new VLA-ROSAT study that probes the magnetic field
strength and distribution over a sample of 16 ``normal'' low redshift (z < 0.1)
galaxy clusters. The clusters span two orders of magnitude in X-ray luminosity,
and were selected to be free of (unusual) strong radio cluster halos, and
widespread cooling flows. Consistent with these criteria, most clusters show a
relaxed X-ray morphology and little or no evidence for recent merger activity.
Analysis of the rotation measure (RM) data shows cluster-generated Faraday RM
excess out to ~0.5 Mpc from cluster centers. The results, combined with RM
imaging of cluster-embedded sources and ROSAT X-ray profiles indicates that the
hot intergalactic gas within these ``normal'' clusters is permeated with a high
filling factor by magnetic fields at levels of = 5-10 (l/10 kpc)^{-1/2}
microGauss, where l is the field correlation length. These results lead to a
global estimate of the total magnetic energy in clusters, and give new insight
into the ultimate energy origin, which is likely gravitational. These results
also shed some light on the cluster evolutionary conditions that existed at the
onset of cooling flows.Comment: 6 pages, 1 figure, uses emulateapj5.sty, accepted by ApJ
Dipolarization Fronts in the Jovian Magnetotail: Statistical Survey of Ion Intensity Variations Using Juno Observations
Energetic particle acceleration and energization in planetary magnetotails are often associated with dipolarization fronts characterized by a rapid increase of the meridional component of the magnetic field. Despite many studies of dipolarization events in Earth's magnetotail, Jupiter’s magnetotail provides an almost ideal environment to study high-energetic ion acceleration by dipolarization fronts because of its large spatial scales and plasma composition of heavy and light ions. In this study, we focus on the response of different high-energetic ion intensities (H, He, S, and O) to prominent magnetic dipolarization fronts inside the Jovian magnetotail. We investigate if ion energization and acceleration are present in the observations around the identified dipolarization fronts. Therefore, we present a statistical study of 87 dipolarization front signatures, which are identified in the magnetometer data of the Juno spacecraft from July 2016 to July 2021. For the ion intensity analysis, we use the energetic particle observations from the Jupiter Energetic Particle Detector Instrument. Our statistical study reveals that less than half of the identified events are accompanied by an increase of the ion intensities, while most of the other events show no significant change in the ion intensity dynamics. In about 40% of the events located in the dawn sector a significant decrease of the energy spectral index is detected indicating ion acceleration by the dipolarization fronts
A summary of observational records on periodicities above the rotational period in the Jovian magnetosphere
The Jovian magnetosphere is a very dynamic system. The plasma mass-loading from the moon Io and the fast planetary rotation lead to regular release of mass from the Jovian magnetosphere and to a change of the magnetic topology. These regular variations, most commonly on several (2.5–4) days scale, were derived from various data sets obtained by different spacecraft missions and instruments ranging from auroral images to in situ measurements of magnetospheric particles. Specifically, ion measurements from the Galileo spacecraft represent the periodicities, very distinctively, namely the periodic thinning of the plasma sheet and subsequent dipolarization, and explosive mass release occurring mainly during the transition between these two phases. We present a review of these periodicities, particularly concentrating on those observed in energetic particle data. The most distinct periodicities are observed for ions of sulfur and oxygen. The periodic topological change of the Jovian magnetosphere, the associated mass-release process and auroral signatures can be interpreted as a global magnetospheric instability with analogies to the two step concept of terrestrial substorms. Different views on the triggering mechanism of this magnetospheric instability are discussed
Detection of microgauss coherent magnetic fields in a galaxy five billion years ago
Magnetic fields play a pivotal role in the physics of interstellar medium in
galaxies, but there are few observational constraints on how they evolve across
cosmic time. Spatially resolved synchrotron polarization maps at radio
wavelengths reveal well-ordered large-scale magnetic fields in nearby galaxies
that are believed to grow from a seed field via a dynamo effect. To directly
test and characterize this theory requires magnetic field strength and geometry
measurements in cosmologically distant galaxies, which are challenging to
obtain due to the limited sensitivity and angular resolution of current radio
telescopes. Here, we report the cleanest measurements yet of magnetic fields in
a galaxy beyond the local volume, free of the systematics traditional
techniques would encounter. By exploiting the scenario where the polarized
radio emission from a background source is gravitationally lensed by a
foreground galaxy at z = 0.439 using broadband radio polarization data, we
detected coherent G magnetic fields in the lensing disk galaxy as seen 4.6
Gyrs ago, with similar strength and geometry to local volume galaxies. This is
the highest redshift galaxy whose observed coherent magnetic field property is
compatible with a mean-field dynamo origin.Comment: 29 pages, 5 figures (including Supplementary Information). Published
in Nature Astronomy on August 28, 201
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