1,714 research outputs found
Understanding TTP
This poster for the Natural Sciences Poster Session summarizes Thrombotic thrombocytopenic purpura (TTP), a rare autoimmune disorder, either inherited or acquired, that produces antibodies affecting the gene ADAMTS13, which causes bleeding and inhibits blood clotting. Symptoms include purple bruising (purpura) and small red dots on the skin, called petechiae. Untreated TTP can lead to damage in the brain, heart and kidneys
A Study of Cool White Dwarfs in the Sloan Digital Sky Survey Data Release 12
In this work we study white dwarfs where to compare the differences in the
cooling of DAs and non-DAs and their formation channels. Our final sample is
composed by nearly DAs and more than non-DAs that are
simultaneously in the SDSS DR12 spectroscopic database and in the \textit{Gaia}
survey DR2. We present the mass distribution for DAs, DBs and DCs, where it is
found that the DCs are more massive than DAs and
DBs on average. Also we present the photometric effective temperature
distribution for each spectral type and the distance distribution for DAs and
non-DAs. In addition, we study the ratio of non-DAs to DAs as a function of
effective temperature. We find that this ratio is around for
effective temperature above and increases by a factor
of five for effective temperature cooler than . If we assume
that the increase of non-DA stars between to
is due to convective dilution, per cent of
the DAs should turn into non-DAs to explain the observed ratio. Our
determination of the mass distribution of DCs also agrees with the theory that
convective dilution and mixing are more likely to occur in massive white
dwarfs, which supports evolutionary models and observations suggesting that
higher mass white dwarfs have thinner hydrogen layers.Comment: 9 pages, 10 figures, accepted by MNRA
The astrophysical reaction 8Li(n,gamma)9Li from measurements by reverse kinematics
We study the breakup of 9Li projectiles in high energy (28.5 MeV/u)
collisions with heavy nuclear targets (208Pb). The wave functions are
calculated using a single-particle model for 9Li, and a simple optical
potential model for the scattering part. A good agreement with measured data is
obtained with insignificant E2 contribution.Comment: 4 pages, 3 figure
Determination of S17(0) from published data
The experimental landscape for the 7Be+p radiative capture reaction is
rapidly changing as new high precision data become available. We present an
evaluation of existing data, detailing the treatment of systematic errors and
discrepancies, and show how they constrain the astrophysical S factor (S17),
independent of any nuclear structure model. With theoretical models robustly
determining the behavior of the sub-threshold pole, the extrapolation error can
be reduced and a constraint placed on the slope of S17. Using only radiative
capture data, we find S17(0) = 20.7 +/- 0.6 (stat) +/- 1.0 (syst) eV b if data
sets are completely independent, while if data sets are completely correlated
we find S17(0) = 21.4 +/- 0.5 (stat) +/- 1.4 (syst) eV b. The truth likely lies
somewhere in between these two limits. Although we employ a formalism capable
of treating discrepant data, we note that the central value of the S factor is
dominated by the recent high precision data of Junghans et al., which imply a
substantially higher value than other radiative capture and indirect
measurements. Therefore we conclude that further progress will require new high
precision data with a detailed error budget.Comment: 10 pages, 1 figure published versio
The sdA problem - II. Photometric and Spectroscopic Follow-up
Subdwarf A star (sdA) is a spectral classification given to objects showing
H-rich spectra and sub-main sequence surface gravities, but effective
temperature lower than the zero-age horizontal branch. Their evolutionary
origin is an enigma. In this work, we discuss the results of follow-up
observations of selected sdAs. We obtained time resolved spectroscopy for 24
objects, and time-series photometry for another 19 objects. For two targets, we
report both spectroscopy and photometry observations. We confirm seven objects
to be new extremely-low mass white dwarfs (ELMs), one of which is a known
eclipsing star. We also find the eighth member of the pulsating ELM class.Comment: Accepted for publication in MNRAS. 19 pages, 30 figures, 6 table
Comment about constraints on nanometer-range modifications to gravity from low-energy neutron experiments
A topic of present interest is the application of experimentally observed
quantum mechanical levels of ultra-cold neutrons in the earth's gravitational
field for searching short-range modifications to gravity. A constraint on new
forces in the nanometer-range published by Nesvizhevsky and Protasov follows
from inadequate modelling of the interaction potential of a neutron with a
mirror wall. Limits by many orders of magnitude better were already derived
long ago from the consistency of experiments on the neutron-electron
interaction.Comment: three page
The Chemical Composition of an Extrasolar Minor Planet
We report the relative abundances of 17 elements in the atmosphere of the
white dwarf star GD 362, material that, very probably, was contained previously
in a large asteroid or asteroids with composition similar to the Earth/Moon
system. The asteroid may have once been part of a larger parent body not unlike
one of the terrestrial planets of our solar system.Comment: ApJ, in pres
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