scholarly journals A Method for the Determination of 3-D Velocity Fields of Disappearing Solar Filaments

2003 ◽  
Vol 55 (2) ◽  
pp. 503-518 ◽  
Author(s):  
Taro Morimoto ◽  
Hiroki Kurokawa
Keyword(s):  
Velocity Fields ◽  
Solar Filaments

Large-scale Motion of Solar Filaments

2000 ◽  
Vol 179 ◽  
pp. 205-208
Author(s):  
Pavel Ambrož ◽  
Alfred Schroll
Keyword(s):  
Magnetic Flux ◽  
Proper Motion ◽  
Time Scale ◽  
Large Scale ◽  
Accuracy Of Measurements ◽  
Solar Filaments ◽  
General Movement ◽  
Scale Motion ◽  
Velocity Scatter

AbstractPrecise measurements of heliographic position of solar filaments were used for determination of the proper motion of solar filaments on the time-scale of days. The filaments have a tendency to make a shaking or waving of the external structure and to make a general movement of whole filament body, coinciding with the transport of the magnetic flux in the photosphere. The velocity scatter of individual measured points is about one order higher than the accuracy of measurements.

scholarly journals Spurious PIV Vector Correction Using Linear Stochastic Estimation

Fluids ◽  
2019 ◽  
Vol 4 (3) ◽  
pp. 139 ◽  
Author(s):  
Daniel Butcher ◽  
Adrian Spencer
Keyword(s):  
Particle Image ◽  
Velocity Fields ◽  
Average Error ◽  
Stochastic Estimation ◽  
Linear Stochastic Estimation ◽  
Statistical Measures ◽  
Image Velocimetry ◽  
Significant Difference ◽  
Bicubic Interpolation

Techniques for the experimental determination of velocity fields such as particle image velocimetry (PIV) can often be hampered by spurious vectors or sparse regions of measurement which may occur due to a number of reasons. Commonly used methods for detecting and replacing erroneous values are often based on statistical measures of the surrounding vectors and may be influenced by further poor data quality in the region. A new method is presented in this paper using Linear Stochastic Estimation for vector replacement (LSEVR) which allows for increased flexibility in situations with regions of spurious vectors. LSEVR is applied to PIV dataset to demonstrate and assess its performance relative to commonly used bilinear and bicubic interpolation methods. For replacement of a single vector, all methods performed well, with LSEVR having an average error of 11% in comparison to 14% and 18% for bilinear and bicubic interpolation respectively. A more significant difference was found in replacement of clusters of vectors which showed average vector angle errors of 10°, 9° and 6° for bilinear, bicubic and LSEVR respectively. Error in magnitude was 3% for both interpolation techniques and 1% for LSEVR showing a clear benefit to using LSEVR for conditions that require multiple clustered vectors to be replaced.

scholarly journals Formation Depths of Spectral Lines in Cepheids

1995 ◽  
Vol 155 ◽  
pp. 373-374
Author(s):  
Michael D. Albrow ◽  
P. L. Cottrell
Keyword(s):  
Spectral Line ◽  
Velocity Fields ◽  
Radial Velocities ◽  
Spectral Lines ◽  
Line Formation ◽  
Ionisation Potential ◽  
Velocity Gradients ◽  
Different Levels ◽  
Line Depth

There has been a number of observational programmes that have endeavoured to investigate the atmospheric velocity fields in Cepheids (e.g., Sanford 1956, Wallerstein et al. 1992, Butler 1993). These studies measured the radial velocities of lines of different strength, excitation and ionisation potential as these provide an indication of line formation at different levels in the atmosphere. From these measurements, the presence of velocity gradients can be inferred, but determination of the magnitude of such gradients requires knowledge of the spectral line depth of formation. Through dynamical modelling we are endeavouring to ascertain what is actually being measured in the above observational programmes.

Seam Weld Positioning for Composite Extrusion

2006 ◽  
Vol 10 ◽  
pp. 101-110 ◽  
Author(s):  
Marco Schikorra ◽  
Matthias Kleiner
Keyword(s):  
Material Flow ◽  
Base Material ◽  
Extrusion Process ◽  
Velocity Fields ◽  
Experimental Investigations ◽  
Local Perturbation ◽  
Seam Weld ◽  
Element Simulation ◽  
Development Area

The production of continuously reinforced profiles by use of aluminium as base material and a reinforcement made of steel or carbon offers a great potential for modern lightweight constructions. Within this scope, they present the potential for an increase in usage of space frame constructions in automotive or aerospace engineering. But with the insertion of reinforcement in the material flow of the extrusion process some problems can occur that are negligible in thee conventional extrusion processes: in the composite development area a significant local perturbation of the material flow is induced that can lead to the induction of high tensile stresses into the reinforcement. Due to this, failures like cracking of the reinforcement elements during the extrusion process has been detected in experimental investigations. A second problem occurring is the necessity of prediction of the seam weld position and prediction of the seam weld quality. The reinforcement can only be induced by bridge dies between two strands and due to this it is always positioned in a seam weld. While in conventional extrusion the seam weld positions is often only an aesthetical problem, now this position mainly influences the extruded profiles properties like moment of inertia. This paper deals with the problem of determination of seam weld position on the example of a double-t-profile extrusion. By use of a coupled thermo-mechanical finite element simulation with the commercial FE code HyperXtrude from Altair the velocity fields of an extrusion process with and without reinforcement were calculated and the resulting material flow was analysed. The numerical results went along with experimental investigations to verify the calculated results.

Extension of a Method of Solution for Poisson’s Equation

1963 ◽  
Vol 30 (3) ◽  
pp. 415-418 ◽  
Author(s):  
M. H. Cobble ◽  
W. F. Ames
Keyword(s):  
Functional Form ◽  
Fluid Velocity ◽  
Velocity Fields ◽  
Poisson’S Equation ◽  
Coordinate Transformations ◽  
Poisson's Equation ◽  
Method Of Solution ◽  
Substitution Procedure

A classical substitution procedure for solving Poisson’s equation ∇2φ = −K is extended by application of certain coordinate transformations suggested by the functional form of K. The method is applied to the determination of fluid-velocity fields in two curvilinear geometries.

scholarly journals Spectropolarimetric analysis of an active region filament

2019 ◽  
Vol 625 ◽  
pp. A128 ◽  
Author(s):  
C. J. Díaz Baso ◽  
M. J. Martínez González ◽  
A. Asensio Ramos
Keyword(s):  
Magnetic Field ◽  
Magnetic Properties ◽  
Active Region ◽  
Spectral Lines ◽  
Component Model ◽  
Vector Magnetic Field ◽  
Solar Filaments ◽  
Magnetic Filed ◽  
The Magnetic Field

Aims. The determination of the magnetic filed vector in solar filaments is made possible by interpreting the Hanle and Zeeman effects in suitable chromospheric spectral lines like those of the He I multiplet at 10 830 Å. We study the vector magnetic field of an active region filament (NOAA 12087). Methods. Spectropolarimetric data of this active region was acquired with the GRIS instrument at the GREGOR telescope and studied simultaneously in the chromosphere with the He I 10 830 Å multiplet and in the photosphere Si I 10 827 Å line. As has been done in previous studies, only a single-component model was used to infer the magnetic properties of the filament. The results are put into a solar context with the help of the Solar Dynamic Observatory images. Results. Some results clearly point out that a more complex inversion had to be performed. First, the Stokes V map of He I does not show a clear signature of the presence of the filament. Second, the local azimuth map follows the same pattern as Stokes V; it appears that polarity of Stokes V is conditioning the inference to very different magnetic fields even with similar linear polarization signals. This indication suggests that the Stokes V could be dominated from below by the magnetic field coming from the active region, and not from the filament itself. This evidence, and others, will be analyzed in depth and a more complex inversion will be attempted in the second part of this series.

Sign in / Sign up

Export Citation Format

Share Document