scholarly journals Resistive evolution of a force-free plasma to equilibrium

1991 ◽  
Vol 46 (3) ◽  
pp. 437-457
Author(s):  
A. S. Gill ◽  
E. W. Laing
Keyword(s):  
Critical Aspect ◽  
Axial Flux ◽  
Relaxation Theory ◽  
Field Diffusion ◽  
Resistive Plasma ◽  
Maximum Current ◽  
Equilibrium Profiles ◽  
Reversed Field ◽  
Magnetohydrodynamic Model ◽  
Free Plasma

Using the magnetohydrodynamic model, the evolution of a resistive plasma can be represented as a relaxation through a sequence of force-free equilibrium states. We show, by extending existing work, that this process is equivalent to magnetic field diffusion in a strongly anisotropie static conductor. The latter evolution is easier to simulate numerically, and is carried out for laboratory based plasmas confined in cylinders and toroids. We obtain a variety of universal equilibrium profiles that are consistent with experiment and relaxation theory and that predict the existence of states arising in reversed-field pinches. The existence of a critical axial flux is predicted about which there exist stable modes of operation corresponding to high and low current. We also show the existence of a critical aspect ratio at which it is most desirable to build toroidal devices. This corresponds to the value at which maximum current, for a fixed driving field, can be generated.

scholarly journals Dynamo-free plasma in the reversed-field pinch: Advances in understanding the reversed-field pinch improved confinement mode

2005 ◽  
Vol 12 (5) ◽  
pp. 056118 ◽  
Author(s):  
J. K. Anderson ◽  
J. Adney ◽  
A. Almagri ◽  
A. Blair ◽  
D. L. Brower ◽  
...  
Keyword(s):  
Reversed Field Pinch ◽  
Reversed Field ◽  
Free Plasma ◽  
Confinement Mode

Dynamo-free plasma in the reversed field pinch

2004 ◽  
Vol 11 (5) ◽  
pp. L9-L12 ◽  
Author(s):  
J. K. Anderson ◽  
T. M. Biewer ◽  
C. B. Forest ◽  
R. O’Connell ◽  
S. C. Prager ◽  
...  
Keyword(s):  
Reversed Field Pinch ◽  
Reversed Field ◽  
Free Plasma

Infinite contraction in force-free magnetic field evolution in cylindrical geometry

1986 ◽  
Vol 35 (2) ◽  
pp. 273-293 ◽  
Author(s):  
Peter A. Watterson
Keyword(s):  
Blow Up ◽  
Perfect Conductor ◽  
Large Radius ◽  
Axial Flux ◽  
Initial Field ◽  
Cylindrically Symmetric ◽  
Reversed Field ◽  
Self Similar ◽  
Axis Of Symmetry ◽  
New Formulation

This paper provides a new formulation of the resistive force-free evolution of cylindrically symmetric magnetic fields subject to purely radial motions. It is shown analytically that the evolution bounded by a perfect conductor ceases to exist after a finite time if the initial field has total axial flux of opposite sign to the field on the axis of symmetry. A numerical solution indicates that the evolution ceases to exist owing to the unlimited contraction of the field profile producing a line of infinite current density. The asymptotic form of this ‘blow-up’ is identified as the particular self-similar contraction for which the field direction is exactly reversed in the limit of large radius. Possible applications to solar flares and the reversed-field pinch are discussed.

Field Distribution of Strongly Excited Magnetic Lenses

1975 ◽  
Vol 33 ◽  
pp. 140-141
Author(s):  
M. Strojnik
Keyword(s):  
Flux Density ◽  
Field Distribution ◽  
Optical Axis ◽  
Operating Point ◽  
Pole Piece ◽  
Partial Saturation ◽  
Axial Flux ◽  
The Stability

Magnetic lenses operating in partial saturation offer two advantages in HVEM: they exhibit small cs and cc and their power depends little on the excitation IN. Curve H, Fig. 1, shows that the maximal axial flux density Bz max of one of the lenses investigated changes between points (3) and (4) by 5% as the excitation varies by 40%. Consequently, the designer can relax the requirements concerning the stability of the lens current supplies. Saturated lenses, however, can only be used if (i) unwanted fields along the optical axis can be controlled, (ii) 'wobbling' of the optical axis due to inhomogeneous saturation around the pole piece faces is prevented, (iii) ample ampere-turns can be squeezed into the space available, and (iv) the lens operating point covers a sufficient range of accelerating voltages.

Examining the Role of Language in Play Among Children With and Without Developmental Disabilities

2020 ◽  
Vol 51 (3) ◽  
pp. 795-806 ◽  
Author(s):  
Elizabeth J. Short ◽  
Rachael Cooper Schindler ◽  
Rita Obeid ◽  
Maia M. Noeder ◽  
Laura E. Hlavaty ◽  
...  
Keyword(s):  
Developmental Disabilities ◽  
Autism Spectrum ◽  
Free Play ◽  
Group Differences ◽  
Typically Developing ◽  
Play Skills ◽  
Critical Aspect ◽  
Hyperactivity Disorder ◽  
Better Than

Purpose Play is a critical aspect of children's development, and researchers have long argued that symbolic deficits in play may be diagnostic of developmental disabilities. This study examined whether deficits in play emerge as a function of developmental disabilities and whether our perceptions of play are colored by differences in language and behavioral presentations. Method Ninety-three children participated in this study (typically developing [TD]; n = 23, developmental language disorders [DLD]; n = 24, attention-deficit/hyperactivity disorder [ADHD]; n = 26, and autism spectrum disorder [ASD]; n = 20). Children were videotaped engaging in free-play. Children's symbolic play (imagination, organization, elaboration, and comfort) was scored under conditions of both audible language and no audible language to assess diagnostic group differences in play and whether audible language impacted raters' perception of play. Results Significant differences in play were evident across diagnostic groups. The presence of language did not alter play ratings for the TD group, but differences were found among the other diagnostic groups. When language was audible, children with DLD and ASD (but not ADHD) were scored poorly on play compared to their TD peers. When language was not audible, children with DLD were perceived to play better than when language was audible. Conversely, children with ADHD showed organizational deficits when language was not available to support their play. Finally, children with ASD demonstrated poor play performance regardless of whether language was audible or not. Conclusions Language affects our understanding of play skills in some young children. Parents, researchers, and clinicians must be careful not to underestimate or overestimate play based on language presentation. Differential skills in language have the potential to unduly influence our perceptions of play for children with developmental disabilities.

Studies on the Thromboplastic Effect of Human Plasma Lipoproteins

1976 ◽  
Vol 35 (01) ◽  
pp. 178-185 ◽  
Author(s):  
Helena Sandberg ◽  
Lars-Olov Andersson
Keyword(s):  
High Density Lipoprotein ◽  
Human Plasma ◽  
Platelet Rich Plasma ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Plasma Lipoproteins ◽  
Very Low Density Lipoprotein ◽  
Low Density ◽  
Free Plasma ◽  
Good Agreement

SummaryHuman plasma lipoprotein fractions were prepared by flotation in the ultracentrifuge. Addition of these fractions to platelet-rich, platelet-poor and platelet-free plasma affected the partial thromboplastin and Stypven clotting times to various degrees. Addition of high density lipoprotein (HDL) to platelet-poor and platelet-free plasma shortened both the partial thromboplastin and the Stypven time, whereas addition of low density lipoprotein and very low density lipoprotein (LDL + VLDL) fractions only shortened the Stypven time. The additions had little or no effect in platelet-rich plasma.Experiments involving the addition of anti-HDL antibodies to plasmas with different platelet contents and measuring of clotting times produced results that were in good agreement with those noted when lipoprotein was added. The relation between structure and the clot-promoting activity of various phospholipid components is discussed.

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