scholarly journals Diagnostics of Coronal Heating in Solar Active Regions

2004 ◽  
Vol 219 ◽  
pp. 478-482 ◽  
Author(s):  
A. Fludra ◽  
J. Ireland
Keyword(s):  
Magnetic Flux ◽  
Flux Density ◽  
Average Power ◽  
Active Regions ◽  
Coronal Heating ◽  
Magnetic Flux Density ◽  
Line Intensities ◽  
Solar Active Regions ◽  
The Relationship ◽  
Coronal Diagnostic Spectrometer

We study the relationship between EUV spectral line intensities and the photospheric magnetic field in solar active regions, using magnetograms from SOHO-MDI and EUV spectra of the Fe XVI 360.8 Â line (2 × 106 K) and the O V 629.7 A line (220,000 K) from the Coronal Diagnostic Spectrometer on SOHO, recorded for several active regions. We overlay and compare spatial patterns of the O V emission and the magnetic flux concentrations, with a 4″ x 4″ spatial resolution, and search for a relationship between the local O V line intensity and the photospheric magnetic flux density in each active region. While this dependence exhibits a certain amount of scatter, it can be represented by a power law fit. The average power index from all regions is 0.7 ± 0.2. Applying static loop models, we derive the dependence of the heating rate on the magnetic flux density, Eh ∝ B0.8, and compare it to the dependence predicted by the coronal heating models.

scholarly journals Prediction of Inhomogeneous Stress in Metal Structures: A Hybrid Approach Combining Eddy Current Technique and Finite Element Method

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Yating Yu ◽  
Fei Yuan ◽  
Hanchao Li ◽  
Cristian Ulianov ◽  
Guiyun Tian
Keyword(s):  
Finite Element ◽  
Stress Distribution ◽  
Magnetic Flux ◽  
Flux Density ◽  
Eddy Current ◽  
Magnetic Flux Density ◽  
Fe Method ◽  
Metal Structures ◽  
Current Technique ◽  
The Relationship

Concentrated stresses and residual ones are critical for the metal structures’ health, because they can cause microcracks that require emergency maintenance or can result in potential accidents. Therefore, an accurate approach to the measurement of stresses is key for ensuring the health of metal structures. The eddy current technique is an effective approach to detect the stress according to the piezoresistive effect. However, it is limited to detect the surface stress due to the skin effect. In engineering, the stress distribution is inhomogeneous; therefore, to predict the inhomogeneous stress distribution, this paper proposes a nondestructive approach which combines the eddy current technique and finite element (FE) method. The experimental data achieved through the eddy current technique determines the relationship between the applied force and the magnetic flux density, while numerical simulations through the FE method bridge the relationship between the magnetic flux density and the stress distribution in different directions. Therefore, we can predict the inhomogeneous stress nondestructively. As a case study, the applied stress in a three-point-bending simply supported beam was evaluated, and the relative error is less than 8% in the whole beam. This approach can be expected to predict the residual stress in metal structures, such as rail and vehicle structures, if the stress distribution pattern is known.

scholarly journals Properties of Faculae from Observations Near the Opacity Minimum

1994 ◽  
Vol 154 ◽  
pp. 23-27
Author(s):  
P Foukal ◽  
T Moran
Keyword(s):  
Magnetic Flux ◽  
Brightness Temperature ◽  
Flux Density ◽  
Flux Tube ◽  
Angular Resolution ◽  
Negative Contrast ◽  
Active Regions ◽  
Disk Center ◽  
Quantitative Comparison ◽  
Magnetic Flux Density

Imaging of active regions in continuum around 1.6 μm shows that many facular regions are less bright than the photosphere when observed nearer to disk center than μ = cos θ ~ 0.75. The contrast of these dark faculae increases with magnetic flux above a threshold of approximately 2 × 1018 Mx. This explains why not all faculae are dark at 1.6 μm, since the magnetic flux density in many regions of bright Ca K plage emission falls below this threshold. After correction for blurring, the typical contrast value is about 4-5%, so the brightness temperature deficit is about 130 K. Faculae are brighter than the photosphere at 1.63 μm nearer to the limb than μ ~ 0.5. The negative contrast of dark faculae may arise from cooling of the surrounding photosphere, or from increased visibility of cool layers of the facular flux tube itself. Quantitative comparison of these IR data with MHD models awaits calculation of flux tube contrasts at realistic angular resolution.

scholarly journals An Observational Test for Coronal Heating Models

2004 ◽  
Vol 219 ◽  
pp. 473-477
Author(s):  
Lidia van Driel-Gesztelyi ◽  
Pascal Démoulin ◽  
Cristina H. Mandrini ◽  
Louise K. Harra ◽  
James A. Klimchuk
Keyword(s):  
Magnetic Flux ◽  
Flux Density ◽  
Scaling Laws ◽  
Emission Measure ◽  
Coronal Heating ◽  
Mhd Waves ◽  
Magnetic Flux Density ◽  
Coronal Loops ◽  
Coronal Emission ◽  
The Mean

We correlate the evolution of the mean X-ray flux, emission measure and temperature (Yohkoh SXT & BCS) with the magnetic flux density (SOHO/MDI) in active region NOAA 7978 from its birth throughout its decay, for five solar rotations. We show that these plasma parameters together with other quantities deduced from them, such as the density and the pressure, follow power-law relationships with the mean magnetic flux density (B). We derive the dependence of the mean coronal heating rate on the magnetic flux density. We use the obtained scaling laws of coronal loops in thermal equilibrium to derive observational estimates of the scaling of the coronal heating with B. These results are used to test the validity of coronal heating models. We find that models based on the dissipation of stressed, current-carrying magnetic fields are in better agreement with the observations than models that attribute coronal heating to the dissipation of MHD waves injected at the base of the corona. This confirms, with smaller error bars, previous results obtained for individual coronal loops, as well as for the global coronal emission of the Sun and cool stars.

scholarly journals Distributed Magnetic Flux Density on the Cross-Section of a Transformer Core

Electronics ◽  
2019 ◽  
Vol 8 (3) ◽  
pp. 297 ◽  
Author(s):  
Lingzhi Li ◽  
Xuhao Du ◽  
Jie Pan ◽  
Adrian Keating ◽  
David Matthews ◽  
...  
Keyword(s):  
Magnetic Flux ◽  
Flux Density ◽  
Cross Section ◽  
Air Gap ◽  
Magnetic Flux Density ◽  
The Core ◽  
The Cross ◽  
Flux Density Distribution ◽  
Transformer Core ◽  
The Relationship

In this paper, the magnetic flux density distribution on the cross-sections of a transformer core is studied. The core for this study consists of two identical U-shaped cores joint at their open surfaces with known air gaps. The magnetic flux density at one of their joint boundary surfaces was measured for different air gaps. A finite element model (FEM) was built to simulate the magnetic flux density and compared with experiment data. Using the validated FEM, the distributed magnetic flux density on the cross-section of the core structure can be obtained when the air gap approaches zero. An engineering model of the density based on the Ampere’s circuit law was also developed and used to explain the relationship between air gap and mean magnetic flux density on the cross-section. The magnetic flux density on the cross-section was found to have a convex-shaped distribution and could be described by an empirical formula. Using this approach, the magnetic flux density distribution in cores with different interlayer insulation was obtained and discussed. This method could also examine the leakage of magnetic flux density in the air gap region when the distance is non-zero, and the relationship between the leakage field and the field in the core structure. The proposed method and model can provide a more detailed understanding for the magnetic field of transformer cores and potential application in designing quiet transformers and condition monitoring.

scholarly journals An Observational Test for Solar Atmospheric Heating

2001 ◽  
Vol 203 ◽  
pp. 514-516
Author(s):  
L. van Driel-Gesztelyi ◽  
P. Démoulin ◽  
J. Ireland ◽  
B. Thompson ◽  
A. Fludra ◽  
...  
Keyword(s):  
Active Region ◽  
Magnetic Flux ◽  
Flux Density ◽  
Scaling Laws ◽  
Power Laws ◽  
Magnetic Flux Density ◽  
Formation Temperature ◽  
Radio Data ◽  
Multi Wavelength ◽  
The Relationship

We study the evolution of the emissivity correlated with magnetic flux density of an active region from its birth until its decay throughout all atmospheric layers. We analyse multi-wavelength data obtained from SOHO, Yohkoh, GOES, SOLSTICE and 10.7 cm radio data from DRAO, Canada. We utilise our results to understand the scaling laws in different atmospheric layers. We confirm that the relationship between the emitted excess flux (flux - basal flux) and photospheric magnetic flux density ΔF(< f B >) follow power laws, and the powers depend on the formation temperature of the line(s) involved.

scholarly journals Design of a New 1D Halbach Magnet Array with Good Sinusoidal Magnetic Field by Analyzing the Curved Surface

Sensors ◽  
2021 ◽  
Vol 21 (7) ◽  
pp. 2522
Author(s):  
Guangdou Liu ◽  
Shiqin Hou ◽  
Xingping Xu ◽  
Wensheng Xiao
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Permanent Magnet ◽  
Flux Density ◽  
Permanent Magnets ◽  
Air Gap ◽  
Curved Surface ◽  
Magnetic Flux Density ◽  
Sinusoidal Magnetic Field ◽  
The Magnetic Field

In the linear and planar motors, the 1D Halbach magnet array is extensively used. The sinusoidal property of the magnetic field deteriorates by analyzing the magnetic field at a small air gap. Therefore, a new 1D Halbach magnet array is proposed, in which the permanent magnet with a curved surface is applied. Based on the superposition of principle and Fourier series, the magnetic flux density distribution is derived. The optimized curved surface is obtained and fitted by a polynomial. The sinusoidal magnetic field is verified by comparing it with the magnetic flux density of the finite element model. Through the analysis of different dimensions of the permanent magnet array, the optimization result has good applicability. The force ripple can be significantly reduced by the new magnet array. The effect on the mass and air gap is investigated compared with a conventional magnet array with rectangular permanent magnets. In conclusion, the new magnet array design has the scalability to be extended to various sizes of motor and is especially suitable for small air gap applications.

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