507 research outputs found
Actinide-rich and Actinide-poor -Process Enhanced Metal-Poor Stars do not Require Separate -Process Progenitors
The astrophysical production site of the heaviest elements in the universe
remains a mystery. Incorporating heavy element signatures of metal-poor,
-process enhanced stars into theoretical studies of -process production
can offer crucial constraints on the origin of heavy elements. In this study,
we introduce and apply the "Actinide-Dilution with Matching" model to a variety
of stellar groups ranging from actinide-deficient to actinide-enhanced to
empirically characterize -process ejecta mass as a function of electron
fraction. We find that actinide-boost stars do not indicate the need for a
unique and separate -process progenitor. Rather, small variations of neutron
richness within the same type of -process event can account for all observed
levels of actinide enhancements. The very low-, fission-cycling ejecta of
an -process event need only constitute 10-30% of the total ejecta mass to
accommodate most actinide abundances of metal-poor stars. We find that our
empirical distributions of ejecta are similar to those inferred from
studies of GW170817 mass ejecta ratios, which is consistent with neutron-star
mergers being a source of the heavy elements in metal-poor, -process
enhanced stars.Comment: 14 pages, 11 figures, Submitted to Ap
Disorders of Sex Development: Lessons to be Learned from Studies of Spina Bifida and Craniofacial Conditions
Superheavy Elements in Kilonovae
As LIGO-Virgo-KAGRA enters its fourth observing run, a new opportunity to
search for electromagnetic counterparts of compact object mergers will also
begin. The light curves and spectra from the first "kilonova" associated with a
binary neutron star binary (NSM) suggests that these sites are hosts of the
rapid neutron capture ("") process. However, it is unknown just how robust
elemental production can be in mergers. Identifying signposts of the production
of particular nuclei is critical for fully understanding merger-driven
heavy-element synthesis. In this study, we investigate the properties of very
neutron rich nuclei for which superheavy elements () can be produced
in NSMs and whether they can similarly imprint a unique signature on kilonova
light-curve evolution. A superheavy-element signature in kilonovae represents a
route to establishing a lower limit on heavy-element production in NSMs as well
as possibly being the first evidence of superheavy element synthesis in nature.
Favorable NSMs conditions yield a mass fraction of superheavy elements is
at 7.5 hours post-merger. With this mass
fraction of superheavy elements, we find that kilonova light curves may appear
similar to those arising from lanthanide-poor ejecta. Therefore, photometric
characterizations of superheavy-element rich kilonova may possibly misidentify
them as lanthanide-poor events.Comment: 9 pages, 5 figure
Optimism as a Candidate Health Asset: Exploring Its Links With Adolescent Quality of Life in Sweden
Exploring the Role of Practical Wisdom in Addressing Adolescent Childrearing Dilemmas
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154376/1/fare12400.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154376/2/fare12400_am.pd
The presence of extracellular matrix degrading metalloproteinases during fetal development of the intervertebral disc
Matrix metalloproteinases (MMPs) regulate connective tissue architecture and cell migration through extracellular matrix (ECM) degradation and are associated with both physiological and pathological processes. Although they are known to play a role in skeletal development, little is known about the role of MMPs in intervertebral disc (IVD) development. Sixteen fetal human lumbar spine segments, obtained at autopsy, were compared with five normal, non-fetal L4āL5 IVDs. Intensity and/or localization of immunohistochemical staining for MMP-1, -2, -3 and -14 were evaluated by three independent observers. MMP-2 production and activation was quantified by gelatin zymography. MMP-1 and -14 were abundantly present in the nucleus pulposus (NP) and notochordal (NC) cells of the fetal IVDs. In non-fetal IVDs, MMP-1 and -14 staining was significantly less intense (pĀ =Ā 0.001 and pĀ <Ā 0.001, respectively). MMP-3 was found in almost the entire IVD with no significant difference from non-fetal IVDs. MMP-2 staining in the NC and NP cells of the fetal IVD was moderate, but weak in the non-fetal IVD. Gelatin zymography showed a negative correlation of age with MMP-2 activity (pĀ <Ā 0.001). MMP-14 immunostaining correlated positively with MMP-2 activity (pĀ =Ā 0.001). For the first time, the presence of MMP-1, -2, -3 and -14 in the fetal human IVD is shown and the high levels of MMP-1, -2 and -14 suggest a role in the development of the IVD. In particular, the gradual decrease in MMP-2 activation during gestation pinpoints this enzyme as key player in fetal development, possibly through activation by MMP-1 and -14
The r-Process Pattern of a Bright, Highly r-Process-Enhanced, Metal-Poor Halo Star at [Fe/H] ~ -2
A high-resolution spectroscopic analysis is presented for a new highly
r-process-enhanced ([Eu/Fe] = 1.27, [Ba/Eu] = -0.65), very metal-poor ([Fe/H] =
-2.09), retrograde halo star, RAVE J153830.9-180424, discovered as part of the
R-Process Alliance survey. At V = 10.86, this is the brightest and most
metal-rich r-II star known in the Milky Way halo. Its brightness enables
high-S/N detections of a wide variety of chemical species that are mostly
created by the r-process, including some infrequently detected lines from
elements like Ru, Pd, Ag, Tm, Yb, Lu, Hf, and Th, with upper limits on Pb and
U. This is the most complete r-process census in a very metal-poor r-II star.
J1538-1804 shows no signs of s-process contamination, based on its low [Ba/Eu]
and [Pb/Fe]. As with many other r-process-enhanced stars, J1538-1804's
r-process pattern matches that of the Sun for elements between the first,
second, and third peaks, and does not exhibit an actinide boost.
Cosmo-chronometric age-dating reveals the r-process material to be quite old.
This robust main r-process pattern is a necessary constraint for r-process
formation scenarios (of particular interest in light of the recent neutron star
merger, GW 170817), and has important consequences for the origins of r-II
stars. Additional r-I and r-II stars will be reported by the R-Process Alliance
in the near future.Comment: Accepted for publication in ApJ letter
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