1,417 research outputs found
Validated helioseismic inversions for 3-D vector flows
According to time-distance helioseismology, information about internal fluid
motions is encoded in the travel times of solar waves. The inverse problem
consists of inferring 3-D vector flows from a set of travel-time measurements.
Here we investigate the potential of time-distance helioseismology to infer 3-D
convective velocities in the near-surface layers of the Sun. We developed a new
Subtractive Optimally Localised Averaging (SOLA) code suitable for pipeline
pseudo-automatic processing. Compared to its predecessor, the code was improved
by accounting for additional constraints in order to get the right answer
within a given noise level. The main aim of this study is to validate results
obtained by our inversion code. We simulate travel-time maps using a snapshot
from a numerical simulation of solar convective flows, realistic Born
travel-time sensitivity kernels, and a realistic model of travel-time noise.
These synthetic travel times are inverted for flows and the results compared
with the known input flow field. Additional constraints are implemented in the
inversion: cross-talk minimization between flow components and spatial
localization of inversion coefficients. Using modes f, p1 through p4, we show
that horizontal convective flow velocities can be inferred without bias, at a
signal-to-noise ratio greater than one in the top 3.5 Mm, provided that
observations span at least four days. The vertical component of velocity (v_z),
if it were to be weak, is more difficult to infer and is seriously affected by
cross-talk from horizontal velocity components. We emphasise that this
cross-talk must be explicitly minimised in order to retrieve v_z in the top 1
Mm. We also show that statistical averaging over many different areas of the
Sun allows for reliably measuring of average properties of all three flow
components in the top 5.5 Mm of the convection zone.Comment: 14 pages main paper, 9 pages electronic supplement, 28 figures.
Accepted for publication in Astronomy & Astrophysic
Probing sunspots with two-skip time-distance helioseismology
Previous helioseismology of sunspots has been sensitive to both the
structural and magnetic aspects of sunspot structure. We aim to develop a
technique that is insensitive to the magnetic component so the two aspects can
be more readily separated. We study waves reflected almost vertically from the
underside of a sunspot. Time-distance helioseismology was used to measure
travel times for the waves. Ray theory and a detailed sunspot model were used
to calculate travel times for comparison. It is shown that these large distance
waves are insensitive to the magnetic field in the sunspot. The largest travel
time differences for any solar phenomena are observed. With sufficient modeling
effort, these should lead to better understanding of sunspot structure
Greater Forearm Blood Flow is Associated With Higher Physical Activity in Older Individuals
Please refer to the pdf version of the abstract located adjacent to the title
Phylogenetics of Paniceae (Poaceae)
Paniceae demonstrate unique variability of photosynthetic physiology and anatomy, including both non-Kranz and Kranz species
and all subtypes of the latter. This variability suggests hypotheses of independent origin or reversals (e.g., from C4 to C3). These
hypotheses can be tested by phylogenetic analysis of independent molecular characters. The molecular phylogeny of 57 species of
Paniceae was explored using sequences from the grass-specific insert found in the plastid locus rpoC2. Phylogenetic analyses confirmed
some long-recognized alliances in Paniceae, some recent molecular phylogenetic results, and suggested new relationships. Broadly,
Paniceae were found to be paraphyletic with Andropogoneae, Panicum was found to be polyphyletic, and Oplismenus hirtellus was
resolved as the sister group to the remaining ingroup species. A particularly well-supported clade in the rpoC2 tree included four
genera with non-Kranz species and three with distinctively keeled paleas. As previously suggested, the PCK (phosphoenol pyruvate
carboxykinase) C4 subtype arose once within Paniceae. All clades with non-Kranz species had Kranz ancestors or sister taxa suggesting
repeated loss of the Kranz syndrome
State Legislative Update
The purpose of this Bill is to provide an alternative approach for individuals with a cause of action against a municipality.\u27 Rather than the costly and time-consuming traditional method of hiring an attorney and filing a lawsuit, House Bill 2631 offers individuals an opportunity for Alternative Dispute Resolution ( ADR ) in the form of arbitration. The Bill would allow any individual with a claim in contract or tort against a municipality to require the municipality to submit to the arbitration of the claim. The purpose of House Bill 2631 is to facilitate the resolution of individual claims against a city. However, a fundamental principle of arbitration is that it is a matter of contract, and no party should be forced into the arbitration of a claim which they have not agreed to arbitrate
Parents' Sense of “Entitlement” in Adoptive and Nonadoptive Families
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72242/1/j.1545-5300.1996.00441.x.pd
Balltracking: an highly efficient method for tracking flow fields
We present a method for tracking solar photospheric flows that is highly efficient, and demonstrate it using high resolution MDI continuum images. The method involves making a surface from the photospheric granulation data, and allowing many small floating tracers or balls to be moved around by the evolving granulation pattern. The results are tested against synthesised granulation with known flow fields and compared to the results produced by Local Correlation tracking (LCT). The results from this new method have similar accuracy to those produced by LCT. We also investigate the maximum spatial and temporal resolution of the velocity field that it is possible to extract, based on the statistical properties of the granulation data. We conclude that both methods produce results that are close to the maximum resolution possible from granulation data. The code runs very significantly faster than our similarly optimised LCT code, making real time applications on large data sets possible. The tracking method is not limited to photospheric flows, and will also work on any velocity field where there are visible moving features of known scale length
Scattering of the f-mode by small magnetic flux elements from observations and numerical simulations
The scattering of f-modes by magnetic tubes is analyzed using
three-dimensional numerical simulations. An f-mode wave packet is propagated
through a solar atmosphere embedded with three different flux tube models which
differ in radius and total magnetic flux. A quiet Sun simulation without a tube
present is also performed as a reference. Waves are excited inside the flux
tube and propagate along the field lines, and jacket modes are generated in the
surroundings of the flux tube, carrying 40% as much energy as the tube modes.
The resulting scattered wave is mainly an f-mode composed of a mixture of m=0
and m=+/-1 modes. The amplitude of the scattered wave approximately scales with
the magnetic flux. A small amount of power is scattered into the p_1-mode. We
have evaluated the absorption and phase shift from a Fourier-Hankel
decomposition of the photospheric vertical velocities. They are compared with
the results obtained from the emsemble average of 3400 small magnetic elements
observed in high-resolution MDI Doppler datacubes. The comparison shows that
the observed dependence of the phase shift with wavenumber can be matched
reasonably well with the simulated flux tube model. The observed variation of
the phase-shifts with the azimuthal order appears to depend on details of
the ensemble averaging, including possible motions of the magnetic elements and
asymmetrically shaped elements.Comment: Accepted for publication in The Astrophysical Journa
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