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$^{3+}$ 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)]=0.12$\pm$0.27 and [Kr/(O, Ar)]=0.82$\pm$0.29, 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 “output” 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 ‘Europe’ and ‘the European project’. 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 ‘common European heritage’ provided a rationale for the development of the European Union. Now, the emergence of ‘new’ 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 ‘emergencies’; 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