scholarly journals 17. Some considerations on thermal conduction and magnetic fields in prominences

1958 ◽  
Vol 6 ◽  
pp. 150-157 ◽  
Author(s):  
S. Rosseland ◽  
E. Jensen ◽  
E. Tandberg-Hanssen
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Temperature Region ◽  
Thermal Conduction ◽  
Order Of Magnitude ◽  
Long Life

Prominences which extend into the million degree temperature region of the corona will, in the absence of magnetic fields, be heated up to temperatures of the same order of magnitude in the course of at most a few hours. A magnetic field of reasonable magnitude inside the prominence, will, however, be sufficient to cut down thermal conduction and turbulence to such an extent that the long life of some prominences seems understandable.

scholarly journals Observations of magnetic fields in Herbig Ae/Be stars

2018 ◽  
Vol 14 (A30) ◽  
pp. 123-123
Author(s):  
Markus Schöller ◽  
Swetlana Hubrig
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
T Tauri Stars ◽  
Be Stars ◽  
T Tauri ◽  
Weak Magnetic Fields ◽  
Order Of Magnitude ◽  
Field Geometry ◽  
Herbig Ae Stars ◽  
Magnetospheric Accretion

AbstractModels of magnetically driven accretion reproduce many observational properties of T Tauri stars. For the more massive Herbig Ae/Be stars, the corresponding picture has been questioned lately, in part driven by the fact that their magnetic fields are typically one order of magnitude weaker. Indeed, the search for magnetic fields in Herbig Ae/Be stars has been quite time consuming, with a detection rate of about 10% (e.g. Alecian et al. 2008), also limited by the current potential to detect weak magnetic fields. Over the last two decades, magnetic fields were found in about twenty objects (Hubrig et al. 2015) and for only two Herbig Ae/Be stars was the magnetic field geometry constrained. Ababakr, Oudmaijer & Vink (2017) studied magnetospheric accretion in 56 Herbig Ae/Be stars and found that the behavior of Herbig Ae stars is similar to T Tauri stars, while Herbig Be stars earlier than B7/B8 are clearly different. The origin of the magnetic fields in Herbig Ae/Be stars is still under debate. Potential scenarios include the concentration of the interstellar magnetic field under magnetic flux conservation, pre-main-sequence dynamos during convective phases, mergers, or common envelope developments. The next step in this line of research will be a dedicated observing campaign to monitor about two dozen HAeBes over their rotation cycle.

The lunar dynamo

Science ◽  
2014 ◽  
Vol 346 (6214) ◽  
pp. 1246753 ◽  
Author(s):  
Benjamin P. Weiss ◽  
Sonia M. Tikoo
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
The Moon ◽  
Planetary Interiors ◽  
Mechanical Stirring ◽  
Lunar Rocks ◽  
Order Of Magnitude ◽  
Global Magnetic Field ◽  
Dynamo Process ◽  
Inductive Generation

The inductive generation of magnetic fields in fluid planetary interiors is known as the dynamo process. Although the Moon today has no global magnetic field, it has been known since the Apollo era that the lunar rocks and crust are magnetized. Until recently, it was unclear whether this magnetization was the product of a core dynamo or fields generated externally to the Moon. New laboratory and spacecraft measurements strongly indicate that much of this magnetization is the product of an ancient core dynamo. The dynamo field persisted from at least 4.25 to 3.56 billion years ago (Ga), with an intensity reaching that of the present Earth. The field then declined by at least an order of magnitude by ∼3.3 Ga. The mechanisms for sustaining such an intense and long-lived dynamo are uncertain but may include mechanical stirring by the mantle and core crystallization.

Effects of DC and AC Magnetic Fields on Grain Growth in Electrodeposited Nanocrystalline Nickel

2003 ◽  
Vol 788 ◽  
Author(s):  
T. Matsuzaki ◽  
T. Yamada ◽  
K. Jyuami ◽  
S. Tsurekawa ◽  
T. Watanabe ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Grain Growth ◽  
Temperature Region ◽  
Incubation Time ◽  
The Other ◽  
Grain Structure ◽  
Nanocrystalline Nickel ◽  
Magnetic Annealing ◽  
Dc Magnetic Field

ABSTRACTThe effects of DC and AC magnetic fields on grain growth in electrodeposited nanocrystalline nickel were studied. Magnetic annealing was conducted at 573K in the ferromagnetic temperature region and at 693K in the paramagnetic temperature region. Both DC and AC magnetic annealing could enhance the grain growth and produced a homogeneous grain structure at 573K. On the other hand, AC magnetic annealing shortened the incubation time for the late stage abnormal grain growth at 693K in the paramagnetic temperature region, while DC magnetic field could not affect the incubation time.

scholarly journals Thermal conduction effects on formation of chromospheric solar tadpole-like jets

2020 ◽  
Vol 500 (3) ◽  
pp. 3329-3334
Author(s):  
Anamaría Navarro ◽  
F D Lora-Clavijo ◽  
K Murawski ◽  
Stefaan Poedts
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Thermal Conduction ◽  
Mhd Equations ◽  
Temperature Model ◽  
Mass Fluxes ◽  
Parametric Studies ◽  
Atmospheric State ◽  
The Magnetic Field ◽  
The Ideal

ABSTRACT We measure the effects of non-isotropic thermal conduction on generation of solar chromospheric jets through numerical simulations carried out with the use of one fluid magnetohydrodynamics (MHD) code magnus. Following the work of Srivastava et al. (2018), we consider the atmospheric state with a realistic temperature model and generate the ejection of plasma through a gas pressure driver operating in the top chromosphere. We consider the magnetic field mimicking a flux tube and perform parametric studies by varying the magnetic field strength and the amplitude of the driver. We find that in the case of thermal conduction the triggered jets exhibit a considerably larger energy and mass fluxes and their shapes are more collimated and penetrate more the solar corona than for the ideal MHD equations. Low magnetic fields allow these jets to be more energetic, and larger magnetic fields decrease the enhancement of mass and energy due to the inclusion of the thermal conductivity.

The role of magnetic fields in the early stages of star formation

2018 ◽  
Vol 14 (A30) ◽  
pp. 113-114
Author(s):  
Maud Galametz ◽  
Anaëlle Maury ◽  
Valeska Valdivia
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Magnetic Fields ◽  
Large Scale ◽  
Polarized Emission ◽  
Order Of Magnitude ◽  
Low Mass ◽  
Geometrical Effects ◽  
The Magnetic Field

AbstractMagnetic fields are believed to redistribute part of the angular momentum during the collapse and could explain the order-of-magnitude difference between the angular momentum observed in protostellar envelopes and that of a typical main sequence star. The Class 0 phase is the main accretion phase during which most of the final stellar material is collected on the central embryo. To study the structure of the magnetic fields on 50-2000 au scales during that key stage, we acquired SMA polarization observations (870μm) of 12 low-mass Class 0 protostars. In spite of their low luminosity, we detect dust polarized emission in all of them. We observe depolarization effects toward high-density regions potentially due to variations in alignment efficiency or in the dust itself or geometrical effects. By comparing the misalignment between the magnetic field and the outflow orientation, we show that the B is either aligned or perpendicular to the outflow direction. We observe a coincidence between the misalignment and the presence of large perpendicular velocity gradients and fragmentation in the protostar (Galametz et al. 2018). Our team is using MHD simulations combined with the radiative transfer code POLARIS to produce synthetic maps of the polarized emission. This work is helping us understand how the magnetic field varies from the large-scale to the small-scales, quantify beam-averaging biases and study the variations of the polarization angles as a function of wavelength or the assumption made on the grain alignment (see poster by Valdivia).

scholarly journals Observation of long life plasma generated in a cavity by CO2 lasers

1986 ◽  
Vol 4 (1) ◽  
pp. 17-25 ◽  
Author(s):  
H. Daido ◽  
M. Fujita ◽  
K. Terai ◽  
F. Miki ◽  
K. Nishihara ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Computer Simulations ◽  
Thermal Conduction ◽  
Laser Pulses ◽  
Experimental Results ◽  
Co2 Lasers ◽  
Long Life

Plasmas with long life times (∼20 ns) are generated in a cavity target by intense CO2 laser pulses (2 × 1014W/cm2). The plasma life depends on the configuration of irradiation and target, which may infer thermal conduction inhibition by the laser-generated magnetic field. The experimental results agree with those of computer simulations with magnetic inhibition of thermal conduction.

scholarly journals Pseudo-magnetic field-induced slow carrier dynamics in periodically strained graphene

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Dong-Ho Kang ◽  
Hao Sun ◽  
Manlin Luo ◽  
Kunze Lu ◽  
Melvina Chen ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Superconducting Magnets ◽  
Carrier Dynamics ◽  
Relaxation Processes ◽  
Time Resolved ◽  
Strained Graphene ◽  
Order Of Magnitude ◽  
Probe Spectroscopy ◽  
Physical Phenomena

AbstractThe creation of pseudo-magnetic fields in strained graphene has emerged as a promising route to investigate intriguing physical phenomena that would be unattainable with laboratory superconducting magnets. The giant pseudo-magnetic fields observed in highly deformed graphene can substantially alter the optical properties of graphene beyond a level that can be feasible with an external magnetic field, but the experimental signatures of the influence of such pseudo-magnetic fields have yet to be unveiled. Here, using time-resolved infrared pump-probe spectroscopy, we provide unambiguous evidence for slow carrier dynamics enabled by the pseudo-magnetic fields in periodically strained graphene. Strong pseudo-magnetic fields of ~100 T created by non-uniform strain in  graphene on nanopillars are found to significantly decelerate the relaxation processes of hot carriers by more than an order of magnitude. Our findings offer alternative opportunities to harness the properties of graphene enabled by pseudo-magnetic fields for optoelectronics and condensed matter physics.

scholarly journals The Temperature Dependence of the Magnetization Process of the Kondo Insulator YbB12

Crystals ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 26 ◽  
Author(s):  
Yasuhiro H. Matsuda ◽  
Yoshiki Kakita ◽  
Fumitoshi Iga
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Condensed Matter ◽  
Characteristic Temperature ◽  
Energy Scale ◽  
Kondo Temperature ◽  
Magnetization Process ◽  
Kondo Insulator ◽  
Kondo Insulators ◽  
Order Of Magnitude

The properties of the Kondo insulator in a strong magnetic field are one of the most intriguing subjects in condensed matter physics. The Kondo insulating state is expected to be suppressed by magnetic fields, which results in the dramatic change in the electronic state. We have studied the magnetization process of one of the prototypical Kondo insulators YbB 12 at several temperatures in magnetic fields of up to 80 T. The metamagnetism due to the insulator-metal (IM) transition seen around 50 T was found to become significantly broadened at approximately 30 K. This characteristic temperature T * ≈ 30 K in YbB 12 is an order of magnitude lower than the Kondo temperature T K = 240 K. Our results suggest that there is an energy scale smaller than the Kondo temperature that is important to understanding the nature of Kondo insulators.

Calculated Coronal Magnetic Fields and Their Comparison with the Coronal Structures as Observed during Five Solar Eclipses

1994 ◽  
Vol 144 ◽  
pp. 559-564
Author(s):  
P. Ambrož ◽  
J. Sýkora
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Coronal Magnetic Field ◽  
Coronal Magnetic Fields ◽  
Solar Eclipses ◽  
Coronal Structures

AbstractWe were successful in observing the solar corona during five solar eclipses (1973-1991). For the eclipse days the coronal magnetic field was calculated by extrapolation from the photosphere. Comparison of the observed and calculated coronal structures is carried out and some peculiarities of this comparison, related to the different phases of the solar cycle, are presented.

Radio Measurements of Coronal Magnetic Fields

1994 ◽  
Vol 144 ◽  
pp. 21-28 ◽  
Author(s):  
G. B. Gelfreikh
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Active Regions ◽  
High Sensitivity ◽  
Coronal Magnetic Field ◽  
Transverse Magnetic ◽  
Radio Sources ◽  
Radio Waves ◽  
Solar Active Regions

AbstractA review of methods of measuring magnetic fields in the solar corona using spectral-polarization observations at microwaves with high spatial resolution is presented. The methods are based on the theory of thermal bremsstrahlung, thermal cyclotron emission, propagation of radio waves in quasi-transverse magnetic field and Faraday rotation of the plane of polarization. The most explicit program of measurements of magnetic fields in the atmosphere of solar active regions has been carried out using radio observations performed on the large reflector radio telescope of the Russian Academy of Sciences — RATAN-600. This proved possible due to good wavelength coverage, multichannel spectrographs observations and high sensitivity to polarization of the instrument. Besides direct measurements of the strength of the magnetic fields in some cases the peculiar parameters of radio sources, such as very steep spectra and high brightness temperatures provide some information on a very complicated local structure of the coronal magnetic field. Of special interest are the results found from combined RATAN-600 and large antennas of aperture synthesis (VLA and WSRT), the latter giving more detailed information on twodimensional structure of radio sources. The bulk of the data obtained allows us to investigate themagnetospheresof the solar active regions as the space in the solar corona where the structures and physical processes are controlled both by the photospheric/underphotospheric currents and surrounding “quiet” corona.

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