The pancaking of coronal mass ejections: an in situ attestation

2020 ◽  
Vol 493 (1) ◽  
pp. L16-L21 ◽  
Author(s):  
Anil N Raghav ◽  
Zubair I Shaikh
Keyword(s):  
Cross Section ◽  
Space Weather ◽  
Coronal Mass Ejections ◽  
Arrival Time ◽  
Interplanetary Space ◽  
Morphological Evolution ◽  
Circular Cross Section ◽  
Primary Concern ◽  
The Cross

ABSTRACT The interplanetary counterparts of coronal mass ejections (ICMEs) are the leading driver of severe space weather. Their morphological evolution in interplanetary space and the prediction of their arrival time at Earth are the ultimate focus of space weather studies, because of their scientific and technological effects. Several investigations in the last couple of decades have assumed that ICMEs have a circular cross-section. Moreover, various models have also been developed to understand the morphology of ICMEs based on their deformed cross-section. In fact, simulation studies have suggested that the initial circular cross-section flattens significantly during their propagation in the solar wind and this is referred to as ‘pancaking’. However, an observational verification of this phenmenon is still pending and it will eventually be the primary concern of several morphological models. Here, we report the first unambiguous observational evidence of extreme flattening of the cross-section of ICMEs, similar to pancaking, based on in situ measurements of 30 ICME events. In fact, we conclude that the cross-section of ICME flux ropes transformed into a two-dimensional planar magnetic structure. Such a deformed morphological feature not only alters the prediction of their arrival time but also has significant implications in solar-terrestrial physics, the energy budget of the heliosphere, charged particle energization, turbulence dissipation and enhanced geo-effectiveness, etc.

Using Ghost Fronts to Predict the Arrival Time of CMEs during 13-17 June 2012

2020 ◽  
Author(s):  
Yutian Chi ◽  
Chris Scott ◽  
Chenglong Shen ◽  
Yuming Wang
Keyword(s):  
Coronal Mass Ejections ◽  
Large Scale ◽  
Arrival Time ◽  
Interplanetary Space ◽  
In Situ Measurements ◽  
Magnetized Plasma ◽  
Field Of View ◽  
Physical Boundary

<div> <div> <div>Coronal mass ejections (CME) are large-scale eruptions of magnetized plasma and huge energy through the corona and out into interplanetary space. <div>A mount of CMEs observed by HI-1 cameras present two fronts that are similar in shape but separated by a few degrees in elongation. Scott et al. (2019) interpret the ghost fronts as projections of separate discrete sections of the physical boundary of the  CME. Ghost fronts could provide information about the longitudinal shape of CME in the field of view of Hi- 1, which can be used to improve the forecast of the arrival time of ICME. During 13-15 June 2012, STEREO/SECCHI recorded two successive launched Earth-directed CMEs. Both of the two CMEs show clearly two fronts in HI-1 images. We use the ghost fronts to predict the arrival time of the two CMEs and utility the in-situ measurements from VEX and Wind to verify the accuracy of the prediction of ghost fronts model. </div> </div> </div> </div>

scholarly journals Asymptotic Behavior of Stable Structures Made of Beams

2021 ◽  
Author(s):  
Georges Griso ◽  
Larysa Khilkova ◽  
Julia Orlik ◽  
Olena Sivak
Keyword(s):  
Asymptotic Behavior ◽  
Cross Section ◽  
Cross Sections ◽  
Linear Elasticity ◽  
Circular Cross Section ◽  
Linear Elasticity Theory ◽  
Linear Elastic ◽  
The Cross ◽  
Small Rotation ◽  
Stable Structures

AbstractIn this paper, we study the asymptotic behavior of an $\varepsilon $ ε -periodic 3D stable structure made of beams of circular cross-section of radius $r$ r when the periodicity parameter $\varepsilon $ ε and the ratio ${r/\varepsilon }$ r / ε simultaneously tend to 0. The analysis is performed within the frame of linear elasticity theory and it is based on the known decomposition of the beam displacements into a beam centerline displacement, a small rotation of the cross-sections and a warping (the deformation of the cross-sections). This decomposition allows to obtain Korn type inequalities. We introduce two unfolding operators, one for the homogenization of the set of beam centerlines and another for the dimension reduction of the beams. The limit homogenized problem is still a linear elastic, second order PDE.

scholarly journals Validation of Welding Simulations Using Thermal Strains Measured with DIC

2011 ◽  
Vol 70 ◽  
pp. 129-134 ◽  
Author(s):  
Maarten De Strycker ◽  
Pascal Lava ◽  
Wim Van Paepegem ◽  
Luc Schueremans ◽  
Dimitri Debruyne
Keyword(s):  
Residual Stresses ◽  
Cross Section ◽  
Circular Cross Section ◽  
Welding Process ◽  
Weld Bead ◽  
Image Correlation ◽  
Steel Tubes ◽  
Element Analysis ◽  
Strain Evolution ◽  
The Cross

Residual stresses can affect the performance of steel tubes in many ways and as a result their magnitude and distribution is of particular interest to many applications. Residual stresses in cold-rolled steel tubes mainly originate from the rolling of a flat plate into a circular cross section (involving plastic deformations) and the weld bead that closes the cross section (involving non-uniform heating and cooling). Focus in this contribution is on the longitudinal weld bead that closes the cross section. To reveal the residual stresses in the tubes under consideration, a finite element analysis (FEA) of the welding step in the production process is made. The FEA of the welding process is validated with the temperature evolution of the thermal simulation and the strain evolution for the mechanical part of the analysis. Several methods for measuring the strain evolution are available and in this contribution it is investigated if the Digital Image Correlation (DIC) technique can record the strain evolution during welding. It is shown that the strain evolution obtained with DIC is in agreement with that found by electrical resistance strain gauges. The results of these experimental measuring methods are compared with numerical results from a FEA of the welding process.

scholarly journals The torsion and flexure of shafting with keyways or cracks

1932 ◽  
Vol 138 (836) ◽  
pp. 607-634 ◽  
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Torsional Rigidity ◽  
Circular Cross Section ◽  
Transverse Load ◽  
Torsion Problem ◽  
Circular Section ◽  
Physical Conditions ◽  
The Cross ◽  
Straight Lines

The object of the paper is to investigate the properties of shafts of circular cross-section into which keyways or slits have been cut, first when subjected to torsion, and second when bent by a transverse load at one end. The torsion problem for similar cases has been treated by several writers. Filon has worked out an approximation to the case of a circular section with one or two keyways ; in his method the boundary of the cross-section was a nearly circular ellipse and the boundaries of the keyways were confocal hyperbolas. In particular he considered the case when the hyperbola degenerated into straight lines starting from the foci. The solution for a circular section with one keyway in the form of an orthogonal circle has been obtained by Gronwall. In each case the solution has been obtained by the use of a conformal trans­formation and this method is again used in this paper, the transformations used being ρ = k sn 2 t . ρ = k 1/2 sn t , ρ = k 1/2 sn 1/2 t where ρ = x + iy , t = ξ + i η. No work appears to have been done on the flexure problem which is here worked out for several cases of shafts with slits. 2. Summary of the Problems Treated . We first consider the torsional properties of shafts with one and with two indentations. In particular cases numerical results have been obtained for the stresses at particular points and for the torsional rigidity. The results for one indentation and for two indentations of the same width and approximately the same depth have been compared. We next consider the solution of the torsion problem for one, two or four equal slits of any depth from the surface towards the axis. The values of the stresses have not been worked out in these cases since the stress is infinite at the bottom of the slits. This in stress occurs because the physical conditions are not satisfied at the bottom of the slits, but as had been pointed out by Filon this does not affect the validity of the values of the torsional rigidity. We compare the effect on the torsional rigidity of the shaft of one, two and four slits of the same depth in particular cases. We also compare the results for one slit with those obtained by Filon by another method, and find very good agreement which is illustrated by a graph. The reduction in torsional rigidity due to a semicircular keyway is compared with that due to a slit of approximately the same depth. Finally the distortion of the cross-sections at right angles to the planes is investigated, and in this, several interesting and perhaps unexpected features appear. The relative shift of the two sides of the slits is calculated in several cases.

Modeling the Phonon Transport in Nanowire with Different Cross-Section

2013 ◽  
Vol 401-403 ◽  
pp. 852-855
Author(s):  
Gao Hui Su ◽  
Zi Chun Yang ◽  
Feng Rui Sun
Keyword(s):  
Thermal Conductivity ◽  
Cross Section ◽  
Diffuse Reflection ◽  
Silicon Nanowire ◽  
Circular Cross Section ◽  
Phonon Transport ◽  
Reflection Mode ◽  
Section Shape ◽  
Section Size ◽  
The Cross

The phonon transport in silicon nanowire was simulated by Monte Carlo Method (MCM). The effect on the phonon transport of the boundary reflection mode, cross-section size and cross-section shape was studied. Analysis shows that diffuse reflection can result in phonon accumulation at the circumferential boundary. As the cross-section size decrease, the nonuniformity of the temperature distribution within the cross-section becomes more severe. When the area of the square cross-section silicon nanowire (SCSN) is equal to that of the circular cross-section silicon nanowire (CCSN), the thermal conductivity of them is more close to each other.

scholarly journals The radial width of a Coronal Mass Ejection between 0.1 and 0.4 AU estimated from the Heliospheric Imager on STEREO

2009 ◽  
Vol 27 (11) ◽  
pp. 4349-4358 ◽  
Author(s):  
N. P. Savani ◽  
A. P. Rouillard ◽  
J. A. Davies ◽  
M. J. Owens ◽  
R. J. Forsyth ◽  
...  
Keyword(s):  
Cross Section ◽  
Heliocentric Distance ◽  
Circular Cross Section ◽  
Flux Rope ◽  
Field Of View ◽  
Statistical Surveys ◽  
Mass Ejection ◽  
Best Fit ◽  
Heliospheric Imager

Abstract. On 15–17 February 2008, a CME with an approximately circular cross section was tracked through successive images obtained by the Heliospheric Imager (HI) instrument onboard the STEREO-A spacecraft. Reasoning that an idealised flux rope is cylindrical in shape with a circular cross-section, best fit circles are used to determine the radial width of the CME. As part of the process the radial velocity and longitude of propagation are determined by fits to elongation-time maps as 252±5 km/s and 70±5° respectively. With the longitude known, the radial size is calculated from the images, taking projection effects into account. The radial width of the CME, S (AU), obeys a power law with heliocentric distance, R, as the CME travels between 0.1 and 0.4 AU, such that S=0.26 R0.6±0.1. The exponent value obtained is compared to published studies based on statistical surveys of in situ spacecraft observations of ICMEs between 0.3 and 1.0 AU, and general agreement is found. This paper demonstrates the new opportunities provided by HI to track the radial width of CMEs through the previously unobservable zone between the LASCO field of view and Helios in situ measurements.

Herschel-Bulkley Viscoplastic Flow in Tubes of Non-Circular Cross-Section

2016 ◽  
Author(s):  
Mario F. Letelier ◽  
Dennis A. Siginer ◽  
Felipe Godoy ◽  
César Rosas
Keyword(s):  
Cross Section ◽  
Power Index ◽  
Circular Cross Section ◽  
Shear Thickening ◽  
Shear Thinning ◽  
Equation Of Motion ◽  
Arbitrary Cross Section ◽  
Viscoplastic Flow ◽  
The Cross ◽  
Tube Geometry

Flow of a Herschel-Bulkley (H-B) fluid in tubes of non-circular cross-section in investigated analytically. This study complements results presented in [1] where the equation of motion was solved in tubes of arbitrary cross-section for Bingham type of fluids, and the shapes of plug zones centered on the tube axis and stagnant zones attached to the corners were predicted when the cross-section is triangular and square. In this paper we investigate the effect of the power index in the H-B model on the flow for values greater and lesser than unity, considering thus the shear-thinning and shear-thickening effects, which could not be accounted for with the Bingham model. The equation of motion is solved when the cross-section is an equilateral triangle or a square by means of the shape factor method previously introduced in [2]. Thus, shear-thickening and shear-thinning effects are accounted for and related to the tube geometry in predicting the existence and the extent of undeformed regions in the flow field.

A New Method of Measuring the Cross-Sectional Area of Connective Tissue Structures

1988 ◽  
Vol 110 (2) ◽  
pp. 104-109 ◽  
Author(s):  
N. G. Shrive ◽  
T. C. Lam ◽  
E. Damson ◽  
C. B. Frank
Keyword(s):  
Cross Section ◽  
Rectangular Cross Section ◽  
Cross Sectional Area ◽  
Sectional Area ◽  
Connective Tissues ◽  
Maximum Width ◽  
Cross Sectional ◽  
Elliptical Cross ◽  
The Cross

There appears to be no generally accepted method of measuring in-situ the cross-sectional area of connective tissues, particularly small ones, before mechanical testing. An instrument has therefore been devised to measure the cross-sectional area of one such tissue, the rabbit medial collateral ligament, directly and nondestructively. However, the methodology is general and could be applied to other tissues with appropriate changes in detail. The concept employed in the instrument is to measure the thickness of the tissue as a function of position along the width of the tissue. The plot obtained of thickness versus width position is integrated to provide the cross-sectional area. This area is accurate to within 5 percent, depending mainly on alignment of the instrument and pre-load of the ligament. Results on the mid-substance of the rabbit medial collateral ligaments are repeatable and reproducible. Values of maximum width and thickness are less variable than those obtained with a vernier caliper. The measured area is considerably less than that estimated assuming rectangular cross-section and slightly less than that estimated on the assumption of elliptical cross-section.

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