3,353 research outputs found
Physical properties of solar polar jets: A statistical study with Hinode XRT data
The target of this work is to investigate the physical nature of polar jets
in the solar corona and their possible contribution to coronal heating and
solar wind flow based on the analysis of X-ray images acquired by the Hinode
XRT telescope. We estimate the different forms of energy associated with many
of these small-scale eruptions, in particular the kinetic energy and enthalpy.
Two Hinode XRT campaign datasets focusing on the two polar coronal holes were
selected to analyze the physical properties of coronal jets; the analyzed data
were acquired using a series of three XRT filters. Typical kinematical
properties (e.g., length, thickness, lifetime, ejection rate, and velocity) of
18 jets are evaluated from the observed sequences, thus providing information
on their possible contribution to the fast solar wind flux escaping from
coronal holes. Electron temperatures and densities of polar-jet plasmas are
also estimated using ratios of the intensities observed in different filters.
We find that the largest amount of energy eventually provided to the corona
is thermal. The energy due to waves may also be significant, but its value is
comparatively uncertain. The kinetic energy is lower than thermal energy, while
other forms of energy are comparatively low. Lesser and fainter events seem to
be hotter, thus the total contribution by polar jets to the coronal heating
could have been underestimated so far. The kinetic energy flux is usually
around three times smaller than the enthalpy counterpart, implying that this
energy is converted into plasma heating more than in plasma acceleration. This
result suggests that the majority of polar jets are most likely not escaping
from the Sun and that only cooler ejections could possibly have enough kinetic
energy to contribute to the total solar wind flow.Comment: 21 pages, 10 figures, Submitted and accepted for publishing in
Astronomy and Astrophysics journa
The Abundances of Light Neutron-Capture Elements in Planetary Nebulae III. The Impact of New Atomic Data on Nebular Selenium and Krypton Abundance Determinations
The detection of neutron(n)-capture elements in several planetary nebulae
(PNe) has provided a new means of investigating s-process nucleosynthesis in
low-mass stars. However, a lack of atomic data has inhibited accurate
trans-iron element abundance determinations in astrophysical nebulae. Recently,
photoionization and recombination data were determined for Se and Kr, the two
most widely detected n-capture elements in nebular spectra. We have
incorporated these new data into the photoionization code Cloudy. To test the
atomic data, numerical models were computed for 15 PNe that exhibit emission
lines from multiple Kr ions. We found systematic discrepancies between the
predicted and observed emission lines that are most likely caused by inaccurate
photoionization and recombination data. These discrepancies were removed by
adjusting the Kr--Kr photoionization cross sections within their
cited uncertainties and the dielectronic recombination rate coefficients by
slightly larger amounts. From grids of models spanning the physical conditions
encountered in PNe, we derive new, broadly applicable ionization correction
factor (ICF) formulae for calculating Se and Kr elemental abundances. The ICFs
were applied to our previous survey of near-infrared [Kr III] and [Se IV]
emission lines in 120 PNe. The revised Se and Kr abundances are 0.1-0.3 dex
lower than former estimates, with average values of [Se/(O, Ar)]=0.120.27
and [Kr/(O, Ar)]=0.820.29, but correlations previously found between their
abundances and other nebular and stellar properties are unaffected. We also
find a tendency for high-velocity PNe that can be associated with the Galactic
thick disk to exhibit larger s-process enrichments than low-velocity PNe
belonging to the thin disk population.Comment: 73 pages, 6 figures, 18 tables, accepted for publication in ApJ
Increased surface flashover voltage in microfabricated devices
With the demand for improved performance in microfabricated devices, the
necessity to apply greater electric fields and voltages becomes evident. When
operating in vacuum, the voltage is typically limited by surface flashover
forming along the surface of a dielectric. By modifying the fabrication process
we have discovered it is possible to more than double the flashover voltage.
Our finding has significant impact on the realization of next-generation micro-
and nano-fabricated devices and for the fabrication of on-chip ion trap arrays
for the realization of scalable ion quantum technology
Museums Otherwise: A Compendium of Possible Futures
This book is not a typical academic edited volume. Nor does it subscribe to
the usual dictates of an exhibition catalogue. It does not seek to provide
a comprehensive overview of work on climate change and museums or
claim to have discovered One Quick Trick to Solve the Climate Emergency. Instead, the book reflects the main characteristics of the Reimagining Museums for Climate Action project: it is collaborative, distributed, conversational, subversive, nomadic and, at times, playful. The arguments it
puts forward emerge through dialogue and speculation just as much as
they respond to and build on empirical research. In this sense, the book
is perhaps best seen as a partial and in many ways still evolving artefact
of the Reimagining Museums project. It can be read from cover-to-cover,
or its varied contents can be traversed in a less rigid fashion. It is one
âoutputâ among many, and its main aim is to prompt further transdisciplinary alliances, rather than set out a particular position or manifesto. To this end, the book invites peripatetic readings and strange deviations.
It is anchored by eight concepts that reflect the diversity and creativity
of museums, but it is also motivated by a desire to (re)situate this field
within a broader set of debates on the roots of social and environmental
injustice, and the role of museums in these histories
Rethinking Museums for the Climate Emergency
Cultural and natural heritage are central to âEuropeâ and âthe European projectâ. They were bound up in the emergence of nation-states in the eighteenth and nineteenth centuries, where they were used to justify differences over which border conflicts were fought. Later, the idea of a âcommon European heritageâ provided a rationale for the development of the European Union. Now, the emergence of ânewâ populist nationalisms shows how the imagined past continues to play a role in cultural and social governance, while a series of interlinked social and ecological crises are changing the ways that heritage operates. New discourses and ontologies are emerging to reconfigure heritage for the circumstances of the present and the uncertainties of the future. Taking the current role of heritage in Europe as its starting point, Critical Heritage Studies and the Futures of Europe presents a number of case studies that explore key themes in this transformation. Contributors draw on a range of disciplinary perspectives to consider, variously, the role of heritage and museums in the migration and climate âemergenciesâ; approaches to urban heritage conservation and practices of curating cities; digital and digitised heritage; the use of heritage as a therapeutic resource; and critical approaches to heritage and its management. Taken together, the chapters explore the multiple ontologies through which cultural and natural heritage have actively intervened in redrawing the futures of Europe and the world
U.S. Radio in the 21st Century: Staying the Course in Unknown Territory
This essay examines the development of the radio industry in the United States as it makes its way into the 21st century. Issues of regulation, technology, commerce, and culture are addressed
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