95 research outputs found
Quantification of Impact-Induced Melt Production in Numerical Modeling Revisited
Melting and vaporization of rocks in impact cratering is mostly attributed to be a consequence of shock compression. However, other mechanism such as plastic work and decompression by structural uplift also contribute to melt production. In this study we expand the commonly used method to determine shock-induced melting in numerical models from the peak shock pressure by a new approach to account for additional heating due plastic work and internal friction. We compare our new approach with the straight-forward method to simply quantify melting from the temperature relative to the solidus temperature at any arbitrary point in time in the course of crater formation. This much simpler method does account for plastic work but suffers from reduced accuracy due to numerical diffusion inherent to ongoing advection in impact crater formation models. We demonstrate that our new approach is more accurate than previous methods in particular for quantitative determination of impact melt distribution in final crater structures. In addition, we assess the contribution of plastic work to the overall melt volume and find, that melting is dominated by plastic work for impacts at velocities smaller than 7.5–12.5 km/s in rocks, depending on the material strength. At higher impact velocities shock compression is the dominating mechanism for melting. Here, the conventional peak shock pressure method provides similar results compared with our new model. Our method serves as a powerful tool to accurately determine impact-induced heating in particular at relatively low-velocity impacts
Do Kepler superflare stars really include slowly-rotating Sun-like stars ? - Results using APO 3.5m telescope spectroscopic observations and Gaia-DR2 data -
We report the latest view of Kepler solar-type (G-type main-sequence)
superflare stars, including recent updates with Apache Point Observatory (APO)
3.5m telescope spectroscopic observations and Gaia-DR2 data. First, we newly
conducted APO3.5m spectroscopic observations of 18 superflare stars found from
Kepler 1-min time cadence data. More than half (43 stars) are confirmed to be
"single" stars, among 64 superflare stars in total that have been
spectroscopically investigated so far in this APO3.5m and our previous
Subaru/HDS observations. The measurements of (projected rotational
velocity) and chromospheric lines (Ca II H\&K and Ca II 8542\AA) support the
brightness variation of superflare stars is caused by the rotation of a star
with large starspots. We then investigated the statistical properties of Kepler
solar-type superflare stars by incorporating Gaia-DR2 stellar radius estimates.
As a result, the maximum superflare energy continuously decreases as the
rotation period increases. Superflares with energies
erg occur on old, slowly-rotating Sun-like stars
(25 days) approximately once every 2000--3000 years,
while young rapidly-rotating stars with a few days have
superflares up to erg. The maximum starspot area does not depend on
the rotation period when the star is young, but as the rotation slows down, it
starts to steeply decrease at 12 days for Sun-like
stars. These two decreasing trends are consistent since the magnetic energy
stored around starspots explains the flare energy, but other factors like spot
magnetic structure should also be considered.Comment: 71 pages, 31 figures, 10 tables. Accepted for publication in The
Astrophysical Journal (on March 29, 2019
Starspot Mapping with Adaptive Parallel Tempering. II. Application to TESS Data for M-dwarf Flare Stars AU Microscopii, YZ Canis Minoris, and EV Lacertae
Starspots and stellar flares are indicators of stellar magnetic activity. The magnetic energy stored around spots is thought to be the origin of flares, but the connection is not completely understood. To investigate the relation between spot locations deduced from light curves and the occurrence of flares therein, we perform starspot modeling for the TESS light curves of three M-dwarf flare stars, AU Mic, YZ CMi, and EV Lac, using the code implemented in Paper I. The code enables us to deduce multiple stellar/spot parameters by the adaptive parallel tempering algorithm efficiently. We find that flare occurrence frequency is not necessarily correlated with the rotation phases of the light curve for each star. The result of starspot modeling shows that any spot is always visible to the line of sight in all phases, and we suggest that this can be one of the reasons why there is no or low correlation between rotation phases and flare frequency. In addition, the amplitude and shape of the light curve for AU Mic and YZ CMi have varied in two years between different TESS cycles. The result of starspot modeling suggests that this can be explained by the variations of spot size and latitude
Starspot mapping with adaptive parallel tempering I: Implementation of computational code
Starspots are thought to be regions of locally strong magnetic fields,
similar to sunspots, and they can generate photometric brightness modulations.
To deduce stellar and spot properties, such as spot emergence and decay rates,
we implement computational code for starspot modeling. It is implemented with
an adaptive parallel tempering algorithm and an importance sampling algorithm
for parameter estimation and model selection in the Bayesian framework. For
evaluating the performance of the code, we apply it to synthetic light curves
produced with 3 spots. The light curves are specified in the spot parameters,
such as the radii, intensities, latitudes, longitudes, and emergence/decay
durations. The spots are circular with specified radii and intensities relative
to the photosphere, and the stellar differential rotation coefficient is also
included in the light curves. As a result, stellar and spot parameters are
uniquely deduced. The number of spots is correctly determined: the 3-spot model
is preferable because the model evidence is much greater than that of 2-spot
models by orders of magnitude and more than that of 4-spot model by a more
modest factor, whereas the light curves are produced to have 2 or 1 local
minimum during one equatorial rotation period by adjusting the values of
longitude. The spot emergence and decay rates can be estimated with error less
than an order of magnitude, considering the difference of the number of spots.Comment: 27 pages, 14 figures, 2 tables, accepted for publication in Ap
Effective Dissolution of Biomass in Ionic Liquids by Irradiation of Non-Thermal Atmospheric Pressure Plasma
Biomass was dissolved in ionic liquids under non-thermal atmospheric pressure plasma irradiation. On plasma irradiation, the amount of dissolved biomass in the ionic liquids increased from 15 to 29mg for bagasse and from 26 to 36mg for Japanese cedar. The high solubility was attributed to the deconstruction of the lignin network by active chemical species generated by the plasma. Selective extraction of cellulose from biomass was observed under plasma irradiation. © CSIRO 2017.This study was also partly supported by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science. | Japan Society for the Promotion of Science 日本学術振興
Temporal Evolution of Spatially-Resolved Individual Star Spots on a Planet-Hosting Solar-type Star: Kepler 17
Star spot evolution is visible evidence of the emergence/decay of the
magnetic field on stellar surface, and it is therefore important for the
understanding of the underlying stellar dynamo and consequential stellar
flares. In this paper, we report the temporal evolution of individual star spot
area on the hot-Jupiter-hosting active solar-type star Kepler 17 whose transits
occur every 1.5 days. The spot longitude and area evolution are estimated (1)
from the stellar rotational modulations of Kepler data and (2) from the
brightness enhancements during the exoplanet transits caused by existence of
large star spots. As a result of the comparison, number of spots, spot
locations, and the temporal evolution derived from the rotational modulations
is largely different from those of in-transit spots. We confirm that although
only two light curve minima appear per rotation, there are clearly many spots
present on the star. We find that the observed differential intensity changes
are sometimes consistent with the spot pattern detected by transits, but they
sometimes do not match with each other. Although the temporal evolution derived
from the rotational modulation differs from those of in-transit spots to a
certain degree, the emergence/decay rates of in-transit spots are within an
order of magnitude of those derived for sunspots as well as our previous
research based only on rotational modulations. This supports a hypothesis that
the emergence/decay of sunspots and extremely-large star spots on solar-type
stars occur through the same underlying processes.Comment: 37 pages, 12 figures, 1 table. Accepted for publication in The
Astrophysical Journa
Applicability of radiocolloids, blue dyes and fluorescent indocyanine green to sentinel node biopsy in melanoma
Patients with primary cutaneous melanoma underwent sentinel node (SN) mapping and biopsy at 25 facilities in Japan by the combination of radiocolloid with gamma probe and dye. Technetium-99m (99mTc)-tin colloid, 99mTc-phytate, 2% patent blue violet (PBV) and 0.4% indigo carmine were used as tracers. In some hospitals, 0.5% fluorescent indocyanine green, which allows visualization of the SN with an infrared camera, was concomitantly used and examined. A total of 673 patients were enrolled, and 562 cases were eligible. The detection rates of SN were 95.5% (147/154) with the combination of tin colloid and PBV, 98.9% (368/372) with the combination of phytate and PBV, and 97.2% (35/36) with the combination of tin colloid or phytate and indigo carmine. SN was not detected in 12 cases by the combination method, and the primary tumor was in the head and neck in six of those 12 cases. In eight of 526 cases (1.5%), SN was detected by PBV but not by radiocolloid. There were 13 cases (2.5%) in which SN was detected by radiocolloid but not by PBV. In 18 of 36 cases (50%), SN was detected by radiocolloid but not by indigo carmine. Concomitantly used fluorescent indocyanine green detected SN in all of 67 cases. Interference with transcutaneous oximetry by PVB was observed in some cases, although it caused no clinical trouble. Allergic reactions were not reported with any of the tracers. 99mTc-tin colloid, 99mTc-phytate, PBV and indocyanine green are useful tracers for SN mapping.ArticleJOURNAL OF DERMATOLOGY. 39(4):336-338 (2012)journal articl
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