20,593 research outputs found
Quantitative assessment of Earthās radiation belt modeling
The āQuantitative Assessment of Radiation Belt Modelingā focus group was in place at Geospace Environment Modeling from 2014 to 2018. The overarching goals of this focus group were to bring together the current stateāofātheāart models for the acceleration, transport, and loss processes in Earth's radiation belts; develop eventāspecific and global inputs of wave, plasma, and magnetic field to drive these models; and combine all these components to achieve a quantitative assessment of radiation belt modeling by validating against contemporary radiation belt measurements. This article briefly reviews the current understanding of radiation belt dynamics and related modeling efforts, summarizes the activities and accomplishments of the focus group, and discusses future directions.Accepted manuscrip
Quantitative assessment of radiation belt modeling
The āQuantitative Assessment of Radiation Belt Modelingā focus group was in place at Geospace Environment Modeling from 2014 to 2018. The overarching goals of this focus group were to bring together the current stateāofātheāart models for the acceleration, transport, and loss processes in Earth's radiation belts; develop eventāspecific and global inputs of wave, plasma, and magnetic field to drive these models; and combine all these components to achieve a quantitative assessment of radiation belt modeling by validating against contemporary radiation belt measurements. This article briefly reviews the current understanding of radiation belt dynamics and related modeling efforts, summarizes the activities and accomplishments of the focus group, and discusses future directions.Accepted manuscrip
Radiance and Doppler shift distributions across the network of the quiet Sun
The radiance and Doppler-shift distributions across the solar network provide
observational constraints of two-dimensional modeling of transition-region
emission and flows in coronal funnels. Two different methods, dispersion plots
and average-profile studies, were applied to investigate these distributions.
In the dispersion plots, we divided the entire scanned region into a bright and
a dark part according to an image of Fe xii; we plotted intensities and Doppler
shifts in each bin as determined according to a filtered intensity of Si ii. We
also studied the difference in height variations of the magnetic field as
extrapolated from the MDI magnetogram, in and outside network. For the
average-profile study, we selected 74 individual cases and derived the average
profiles of intensities and Doppler shifts across the network. The dispersion
plots reveal that the intensities of Si ii and C iv increase from network
boundary to network center in both parts. However, the intensity of Ne viii
shows different trends, namely increasing in the bright part and decreasing in
the dark part. In both parts, the Doppler shift of C iv increases steadily from
internetwork to network center. The average-profile study reveals that the
intensities of the three lines all decline from the network center to
internetwork region. The binned intensities of Si ii and Ne viii have a good
correlation. We also find that the large blue shift of Ne viii does not
coincide with large red shift of C iv. Our results suggest that the network
structure is still prominent at the layer where Ne viii is formed in the quiet
Sun, and that the magnetic structures expand more strongly in the dark part
than in the bright part of this quiet Sun region.Comment: 10 pages,9 figure
The role of Joule heating in the formation of nanogaps by electromigration
We investigate the formation of nanogaps in gold wires due to
electromigration. We show that the breaking process will not start until a
local temperature of typically 400 K is reached by Joule heating. This value is
rather independent of the temperature of the sample environment (4.2-295 K).
Furthermore, we demonstrate that the breaking dynamics can be controlled by
minimizing the total series resistance of the system. In this way, the local
temperature rise just before break down is limited and melting effects are
prevented. Hence, electrodes with gaps < 2 nm are easily made, without the need
of active feedback. For optimized samples, we observe quantized conductance
steps prior the gap formation.Comment: including 7 figure
Upflows in the upper transition region of the quiet Sun
We investigate the physical meaning of the prominent blue shifts of Ne VIII,
which is observed to be associated with quiet-Sun network junctions (boundary
intersections), through data analyses combining force-free-field extrapolations
with EUV spectroscopic observations. For a middle-latitude region, we
reconstruct the magnetic funnel structure in a sub-region showing faint
emission in EIT-Fe 195. This funnel appears to consist of several smaller
funnels that originate from network lanes, expand with height and finally merge
into a single wide open-field region. However, the large blue shifts of Ne VIII
are generally not associated with open fields, but seem to be associated with
the legs of closed magnetic loops. Moreover, in most cases significant upflows
are found in both of the funnel-shaped loop legs. These quasi-steady upflows
are regarded as signatures of mass supply to the coronal loops rather than the
solar wind. Our observational result also reveals that in many cases the
upflows in the upper transition region (TR) and the downflows in the middle TR
are not fully cospatial. Based on these new observational results, we suggest
different TR structures in coronal holes and in the quiet Sun.Comment: 4 pages, 4 figures, will appear in the Proceedings of the Solar wind
12 conferenc
Geometric model generation for CFD simulation of blood and air flows
A new adaptive algorithm is developed for the reconstruction of geometric models of carotid arteries and human airways from CT images. Based on the patient-specific geometric models, Computational Fluid Dynamics (CFD) models of patient's blood and air flows are constructed to calculate hemodynamic parameters and particle deposition patterns for patient-specific clinical applications
Non-Hausdorff Symmetries of C*-algebras
Symmetry groups or groupoids of C*-algebras associated to non-Hausdorff
spaces are often non-Hausdorff as well. We describe such symmetries using
crossed modules of groupoids. We define actions of crossed modules on
C*-algebras and crossed products for such actions, and justify these
definitions with some basic general results and examples.Comment: very minor changes. To appear in Math. An
- ā¦