46 research outputs found
Induced four fold anisotropy and bias in compensated NiFe/FeMn double layers
A vector spin model is used to show how frustrations within a multisublattice
antiferromagnet such as FeMn can lead to four-fold magnetic anisotropies acting
on an exchange coupled ferromagnetic film. Possibilities for the existence of
exchange bias are examined and shown to exist for the case of weak chemical
disorder at the interface in an otherwise perfect structure. A sensitive
dependence on interlayer exchange is found for anisotropies acting on the
ferromagnet through the exchange coupling, and we show that a wide range of
anisotropies can appear even for a perfect crystalline structure with an
ideally flat interface.Comment: 7 pages, 7 figure
Abundances of the elements in the solar system
A review of the abundances and condensation temperatures of the elements and
their nuclides in the solar nebula and in chondritic meteorites. Abundances of
the elements in some neighboring stars are also discussed.Comment: 42 pages, 11 tables, 8 figures, chapter, In Landolt- B\"ornstein, New
Series, Vol. VI/4B, Chap. 4.4, J.E. Tr\"umper (ed.), Berlin, Heidelberg, New
York: Springer-Verlag, p. 560-63
Highly Charged Ions in Rare Earth Permanent Magnet Penning Traps
A newly constructed apparatus at the National Institute of Standards and
Technology (NIST) is designed for the isolation, manipulation, and study of
highly charged ions. Highly charged ions are produced in the NIST electron-beam
ion trap (EBIT), extracted through a beamline that selects a single mass/charge
species, then captured in a compact Penning trap. The magnetic field of the
trap is generated by cylindrical NdFeB permanent magnets integrated into its
electrodes. In a room-temperature prototype trap with a single NdFeB magnet,
species including Ne10+ and N7+ were confined with storage times of order 1
second, showing the potential of this setup for manipulation and spectroscopy
of highly charged ions in a controlled environment. Ion capture has since been
demonstrated with similar storage times in a more-elaborate Penning trap that
integrates two coaxial NdFeB magnets for improved B-field homogeneity. Ongoing
experiments utilize a second-generation apparatus that incorporates this
two-magnet Penning trap along with a fast time-of-flight MCP detector capable
of resolving the charge-state evolution of trapped ions. Holes in the
two-magnet Penning trap ring electrode allow for optical and atomic beam
access. Possible applications include spectroscopic studies of one-electron
ions in Rydberg states, as well as highly charged ions of interest in atomic
physics, metrology, astrophysics, and plasma diagnostics.Comment: Proceedings of CDAMOP-2011, 13-16 Dec 2011, Delhi, India. To be
published by Springer Verla
Origins of the Ambient Solar Wind: Implications for Space Weather
The Sun's outer atmosphere is heated to temperatures of millions of degrees,
and solar plasma flows out into interplanetary space at supersonic speeds. This
paper reviews our current understanding of these interrelated problems: coronal
heating and the acceleration of the ambient solar wind. We also discuss where
the community stands in its ability to forecast how variations in the solar
wind (i.e., fast and slow wind streams) impact the Earth. Although the last few
decades have seen significant progress in observations and modeling, we still
do not have a complete understanding of the relevant physical processes, nor do
we have a quantitatively precise census of which coronal structures contribute
to specific types of solar wind. Fast streams are known to be connected to the
central regions of large coronal holes. Slow streams, however, appear to come
from a wide range of sources, including streamers, pseudostreamers, coronal
loops, active regions, and coronal hole boundaries. Complicating our
understanding even more is the fact that processes such as turbulence,
stream-stream interactions, and Coulomb collisions can make it difficult to
unambiguously map a parcel measured at 1 AU back down to its coronal source. We
also review recent progress -- in theoretical modeling, observational data
analysis, and forecasting techniques that sit at the interface between data and
theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue
connected with a 2016 ISSI workshop on "The Scientific Foundations of Space
Weather." 44 pages, 9 figure