The impact of non-ideal effects on the circumstellar disk evolution and their observational signatures

2018 ◽  
Vol 14 (A30) ◽  
pp. 116-116
Author(s):  
Y. Tsukamoto ◽  
S. Okuzumi ◽  
K. Iwasaki ◽  
M. N. Machida ◽  
S. Inutsuka
Keyword(s):  
Magnetic Field ◽  
Hall Effect ◽  
Recent Observation ◽  
Ambipolar Diffusion ◽  
Circumstellar Disk ◽  
Neutral Drift ◽  
Disk Formation ◽  
Evolutionary Phase ◽  
The Impact ◽  
The Magnetic Field

AbstractIt has been recognized that non-ideal MHD effects (Ohmic diffusion, Hall effect, ambipolar diffusion) play crucial roles for the circumstellar disk formation and evolution. Ohmic and ambipolar diffusion decouple the gas and the magnetic field, and significantly reduces the magnetic torque in the disk, which enables the formation of the circumstellar disk (e.g., Tsukamoto et al. 2015b). They set an upper limit to the magnetic field strength of ∼ 0.1 G around the disk (Masson et al. 2016). The Hall effect notably changes the magnetic torques in the envelope around the disk, and strengthens or weakens the magnetic braking depending on the relative orientation of magnetic field and angular momentum. This suggests that the bimodal evolution of the disk size possibly occurs in the early disk evolutionary phase (Tsukamoto et al. 2015a, Tsukamoto et al. 2017). Hall effect and ambipolar diffusion imprint the possibly observable characteristic velocity structures in the envelope of Class 0/I YSOs. Hall effect forms a counter-rotating envelope around the disk. Our simulations show that counter rotating envelope has the size of 100–1000 au and a recent observation actually infers such a structure (Takakuwaet al. 2018). Ambipolar diffusion causes the significant ion-neutral drift in the envelopes. Our simulations show that the drift velocity of ion could become 100-1000 ms–1.

scholarly journals Constraint on ion–neutral drift velocity in the Class 0 protostar B335 from ALMA observations

2018 ◽  
Vol 615 ◽  
pp. A58 ◽  
Author(s):  
Hsi-Wei Yen ◽  
Bo Zhao ◽  
Patrick M. Koch ◽  
Ruben Krasnopolsky ◽  
Zhi-Yun Li ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Drift Velocity ◽  
Large Scale ◽  
Ambipolar Diffusion ◽  
Neutral Drift ◽  
Neutral Gas ◽  
Mhd Simulations ◽  
Ambipolar Drift ◽  
Velocity Drift ◽  
The Magnetic Field

Aims. Ambipolar diffusion can cause a velocity drift between ions and neutrals. This is one of the non-ideal magnetohydrodynamics (MHD) effects proposed to enable the formation of large-scale Keplerian disks with sizes of tens of au. To observationally study ambipolar diffusion in collapsing protostellar envelopes, we compare here gas kinematics traced by ionized and neutral molecular lines and discuss the implication on ambipolar diffusion. Methods. We analyzed the data of the H13CO+ (3–2) and C18O (2–1) emission in the Class 0 protostar B335 obtained with our ALMA observations. We constructed kinematical models to fit the velocity structures observed in the H13CO+ and C18O emission and to measure the infalling velocities of the ionized and neutral gas on a 100 au scale in B335. Results. A central compact (~1′′–2′′) component that is elongated perpendicular to the outflow direction and exhibits a clear velocity gradient along the outflow direction is observed in both lines and most likely traces the infalling flattened envelope. With our kinematical models, the infalling velocities in the H13CO+ and C18O emission are both measured to be 0.85 ± 0.2 km s−1 at a radius of 100 au, suggesting that the velocity drift between the ionized and neutral gas is at most 0.3 km s−1 at a radius of 100 au in B335. Conclusions. The Hall parameter for H13CO+ is estimated to be ≫1 on a 100 au scale in B335, so that H13CO+ is expected to be attached to the magnetic field. Our non-detection or upper limit of the velocity drift between the ionized and neutral gas could suggest that the magnetic field remains rather well coupled to the bulk neutral material on a 100 au scale in this source, and that any significant field-matter decoupling, if present, likely occurs only on a smaller scale, leading to an accumulation of magnetic flux and thus efficient magnetic braking in the inner envelope. This result is consistent with the expectation from the MHD simulations with a typical ambipolar diffusivity and those without ambipolar diffusion. On the other hand, the high ambipolar drift velocity of 0.5–1.0 km s−1 on a 100 au scale predicted in the MHD simulations with an enhanced ambipolar diffusivity by removing small dust grains, where the minimum grain size is 0.1 μm, is not detected in our observations. However, because of our limited angular resolution, we cannot rule out a significant ambipolar drift only in the midplane of the infalling envelope. Future observations with higher angular resolutions (~0. ′′1) are needed to examine this possibility and ambipolar diffusion on a smaller scale.

scholarly journals Imprints of the post-recombination dissipation of helical magnetic field on the Cosmic Microwave Background Radiation

2020 ◽  
pp. 2050122
Author(s):  
Sandhya Jagannathan ◽  
Ramkishor Sharma ◽  
T. R. Seshadri
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Cosmic Microwave Background ◽  
Spectral Index ◽  
Background Radiation ◽  
Power Spectra ◽  
Ambipolar Diffusion ◽  
Microwave Background ◽  
The Impact ◽  
The Magnetic Field

Astrophysical magnetic fields decay primarily via two processes, namely ambipolar diffusion and turbulence. Constraints on the strength and the spectral index of nonhelical magnetic fields have been derived earlier in the literature through the effect of the above-mentioned processes on the cosmic microwave background (CMB) radiation. A helical component of the magnetic field is also produced in various models of magnetogenesis, which can explain larger coherence length magnetic field. In this study, we focus on studying the effects of post-recombination decay of maximally helical magnetic fields through ambipolar diffusion and decaying magnetic turbulence and the impact of this decay on CMB. We find that helical magnetic fields lead to changes in the evolution of baryon temperature and ionization fraction which in turn lead to modifications in the CMB temperature and polarization anisotropy. These modifications are different from those arising due to nonhelical magnetic fields with the changes dependent on the strength and the spectral index of the magnetic field power spectra.

scholarly journals Influence of ambipolar and Hall effects on vorticity in three-dimensional simulations of magneto-convection

2020 ◽  
Vol 379 (2190) ◽  
pp. 20200176 ◽  
Author(s):  
E. Khomenko ◽  
M. Collados ◽  
N. Vitas ◽  
P. A. González-Morales
Keyword(s):  
Magnetic Field ◽  
Hall Effect ◽  
Three Dimensional ◽  
Power Spectra ◽  
Ambipolar Diffusion ◽  
Saturation Regime ◽  
Initial Field ◽  
Poynting Flux ◽  
The Magnetic Field ◽  
Three Dimensional Simulations

This paper presents the results of the analysis of three-dimensional simulations of solar magneto-convection that include the joint action of the ambipolar diffusion and the Hall effect. Three simulation runs are compared: one including both ambipolar diffusion and the Hall effect; one including only ambipolar diffusion and one without any of these two effects. The magnetic field is amplified from initial field to saturation level by the action of turbulent local dynamo. In each of these cases, we study 2 h of simulated solar time after the local dynamo reaches the saturation regime. We analyse the power spectra of vorticity, of magnetic field fluctuations and of the different components of the magnetic Poynting flux responsible for the transport of vertical or horizontal perturbations. Our preliminary results show that the ambipolar diffusion produces a strong reduction of vorticity in the upper chromospheric layers and that it dissipates the vortical perturbations converting them into thermal energy. The Hall effect acts in the opposite way, strongly enhancing the vorticity. When the Hall effect is included, the magnetic field in the simulations becomes, on average, more vertical and long-lived flux tube-like structures are produced. We trace a single magnetic structure to study its evolution pattern and the magnetic field intensification, and their possible relation to the Hall effect. This article is part of the Theo Murphy meeting issue ‘High-resolution wave dynamics in the lower solar atmosphere’.

Influences on Occurrence of Magnetism During Cutting Processes

2011 ◽  
Vol 5 (3) ◽  
pp. 294-299
Author(s):  
Dirk Bähre ◽  
◽  
Kirsten Trapp ◽  
Ralf Tschuncky ◽  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Hall Effect ◽  
Ferromagnetic Materials ◽  
Material Structure ◽  
Time Dependency ◽  
Technological Parameters ◽  
Cutting Processes ◽  
The Impact ◽  
The Magnetic Field

Workpieces from ferromagnetic materials influenced by machining can build magnetic fields, which can cause problems in production or application. One of the assumed causes of magnetism occurring in cutting processes is the change in the material structure due to the impact of the tool. To study these influences, milling tests are carried out. The magnetic field is measured by means of sensors functioning on the basis of the Hall effect. The coherences between geometry, kinematics, technological parameters, time dependency, and the magnetisation characteristics of the workpiece are considered.

MAGNETIC FIELD IMPACT UPON TRIBOTECHNICAL CHARACTERISTICS OF PERMANENT CONNECTIONS IN RELATION TO FRICTION SHOCK ABSORBERS

2020 ◽  
Vol 2020 (10) ◽  
pp. 4-11
Author(s):  
Victor Tikhomirov ◽  
Aleksandr Gorlenko ◽  
Stanislav Volohov ◽  
Mikhail Izmerov
Keyword(s):  
Magnetic Field ◽  
Friction Factor ◽  
Physical Contact ◽  
Active Centers ◽  
Press Fit ◽  
Electro Magnetic Field ◽  
Investigation Methods ◽  
Electro Magnetic ◽  
The Impact ◽  
The Magnetic Field

The work purpose is the investigation of magnetic field impact upon properties of friction steel surfaces at fit stripping with tightness through manifested effects and their wear visually observed. On the spots of a real contact the magnetic field increases active centers, their amount and saturation with the time of dislocation outlet, and has an influence upon tribo-mating. The external electro-magnetic field promotes the increase of the number of active centers at the expense of dislocations outlet on the contact surface, and the increase of a physical contact area results in friction tie strengthening and growth of a friction factor. By the example of friction pairs of a spentonly unit in the suspension of coach cars there is given a substantiation of actuality and possibility for the creation of technical devices with the controlled factor of friction and the stability of effects achieved is also confirmed experimentally. Investigation methods: the fulfillment of laboratory physical experiments on the laboratory plant developed and patented on bush-rod samples inserted with the fit and tightness. The results of investigations and novelty: the impact of the magnetic field upon the value of a stripping force of a press fit with the guaranteed tightness is defined. Conclusion: there is a possibility to control a friction factor through the magnetic field impact upon a friction contact.

scholarly journals Qualitative and quantitative assessment of magnetic vestibular stimulation in humans

2020 ◽  
Vol 30 (6) ◽  
pp. 353-361
Author(s):  
Rebecca S. Dewey ◽  
Rachel Gomez ◽  
Chris Degg ◽  
David M. Baguley ◽  
Paul M. Glover
Keyword(s):  
Magnetic Field ◽  
Objective Measure ◽  
Quantitative Measure ◽  
Vestibular Stimulation ◽  
Initial Study ◽  
Clinical Test ◽  
Healthy Control ◽  
Student’S T ◽  
The Impact ◽  
The Magnetic Field

The sensation of phantom motion or exhibition of bodily sway is often reported in the proximity of an MR scanner. It is proposed that the magnetic field stimulates the vestibular system. There are a number of possible mechanisms responsible, and the relative contributions of susceptibility on the otolithic receptors and the Lorentz force on the cupulae have not yet been explored. This exploratory study aims to investigate the impact of being in the proximity of a 7.0 T MR scanner. The modified clinical test of sensory interaction on balance (mCTSIB) was used to qualitatively ascertain whether or not healthy control subjects who passed the mCTSIB in normal conditions 1) experienced subjective sensations of dizziness, vertigo or of leaning or shifting in gravity when in the magnetic field and 2) exhibited visibly increased bodily sway whilst in the magnetic field compared to outside the magnetic field. Condition IV of the mCTSIB was video recorded outside and inside the magnetic field, providing a semi-quantitative measure of sway. For condition IV of the mCTSIB (visual and proprioceptive cues compromised), all seven locations/orientations around the scanner yielded significantly more sway than at baseline (p < 0.01 FDR). A Student’s t-test comparing the RMS velocity of a motion marker on the upper arm during mCTSIB condition IV showed a significant increase in the amount of motion exhibited in the field (T = 2.59; d.f. = 9; p = 0.029) compared to outside the field. This initial study using qualitative measures of sway demonstrates that there is evidence for MR-naïve individuals exhibiting greater sway while performing the mCTSIB in the magnetic field compared to outside the field. Directional polarity of sway was not significant. Future studies of vestibular stimulation by magnetic fields would benefit from the development of a sensitive, objective measure of balance function, which can be performed inside a magnetic field.

Untersuchung des Druckaufbaus einer stationären, magnetfeldstabilisierten Helium-Entladung mit Hilfe magnetischer Messungen

1967 ◽  
Vol 22 (10) ◽  
pp. 1599-1612 ◽  
Author(s):  
Otto Klüber
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Plasma Column ◽  
Ambipolar Diffusion ◽  
Nernst Effect ◽  
Thermomagnetic Effect ◽  
Field Coil ◽  
Neutral Gas ◽  
Ring Currents ◽  
The Magnetic Field

A stationary discharge is produced bya current flowing parallel to the magnetic field ofa cylindrical coil. In the region where the field is homogeneous the pressure in the plasma column is much higher than that in the surrounding neutral gas. This is mainly caused by diamagnetic ring currents, as is shown by measuring the magnetic flux due to these currents. Two effects are primarily responsible for the ring currents in this region: The already known effect of the ambipolar diffusion across the magnetic field anda thermomagnetic effect, called NERNST effect, whose influence on the pressure build-up ofa plasma has not been investigated hitherto. Other phenomena causing ring currents occur in the plasma near the coil ends and outside the field coil.

Magnetostrictive Self-Diagnosing Smart Bolts

2014 ◽  
Author(s):  
Vladislav Sevostianov
Keyword(s):  
Magnetic Field ◽  
Plastic Deformation ◽  
Magnetic Fields ◽  
Hall Effect ◽  
Stress Level ◽  
Experimental Validation ◽  
Rock Bolts ◽  
Three Point Bending ◽  
Bending Loading ◽  
The Magnetic Field

The paper presents the concept of self-diagnosing smart bolts and its experimental validation. In the present research such bolts are designed, built, and experimentally tested. As a key element of the design, wires of Galfenol (alloy of iron and gallium) are used. This material shows magnetostrictive properties, and, at the same time, is sufficiently ductile to follow typical deformation of rock bolts, and is economically affordable. Two types of Galfenol were used: Ga10Fe90 and Ga17Fe83. The wires have been installed in bolts using two designs — in a drilled central hole or in a cut along the side — and the bolts were tested for generation of the magnetic field under three-point bending loading. To measure the magnetic field in the process of deformation, a magnetometer that utilizes the GMR effect was designed, built, and compared with one utilizing the Hall effect. It is shown that (1) magnetic field generated by deformation of the smart bolts at the stress level of plastic deformation is sufficient to be noticed by the proposed magnetometer; however, the magnetometer using Hall effect is insufficient; (2) Ga10Fe90 produces higher magnetic fields than Ga17Fe83; (3) the magnetic field in plastically bended bolts is relatively stable with time.

scholarly journals The hall effect in liquid electrolytes

1913 ◽  
Vol 88 (606) ◽  
pp. 588-604 ◽  
Keyword(s):  
Magnetic Field ◽  
Hall Effect ◽  
Electric Current ◽  
Metal Plate ◽  
Satisfactory Explanation ◽  
Thermo Electric ◽  
Field Independent ◽  
Set Up ◽  
The Magnetic Field ◽  
Thin Metal Plate

The distortion of the lines of flow of an electric current in a thin metal plate by the action of a magnetic field was discovered in 1879. Hall attributed this to the action of the magnetic field on the molecular currents in the metal film, which were deflected to one side or the other and accompanied by a corresponding twist of the equipotential lines. This explanation did not pass without criticism, and another theory of the effect found by Hall was published in 1884. In that paper the author seeks to explain the effect by assuming a combination of certain mechanical strains and Peltier effects, a thermo-electric current being set up between the strained and the unstrained portions. The effect of such strain was to produce a reverse effect in some metals, and these were precisely the metals for which the Hall effect was found to reverse. Aluminium was the only exception. In other respects, however, as shown by Hall in a later paper, Bidwell's theory did not stand the test of experiment, and the results lend no support to his theory, while they are in complete accordance withe the explanation that the molecular currents are disturbed by the action of the magnetic field. On the electron theory of metallic conduction, the mechanism of the Hall effect is more obvious, but at present no satisfactory explanation of the reversal found in some metals is known. Further experiments have made it clear that there is a real deflection of the elementary currents, due to the application of the magnetic field, independent of any effect due to strain.

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