5,252 research outputs found
Chemical Abundances of the Milky Way Thick Disk and Stellar Halo I.: Implications of [alpha/Fe] for Star Formation Histories in Their Progenitors
We present the abundance analysis of 97 nearby metal-poor (-3.3<[Fe/H]<-0.5)
stars having kinematics characteristics of the Milky Way (MW) thick disk,
inner, and outer stellar halos. The high-resolution, high-signal-to-noise
optical spectra for the sample stars have been obtained with the High
Dispersion Spectrograph mounted on the Subaru Telescope. Abundances of Fe, Mg,
Si, Ca and Ti have been derived using a one-dimensional LTE abundance analysis
code with Kurucz NEWODF model atmospheres. By assigning membership of the
sample stars to the thick disk, inner or outer halo components based on their
orbital parameters, we examine abundance ratios as a function of [Fe/H] and
kinematics for the three subsamples in wide metallicity and orbital parameter
ranges.
We show that, in the metallicity range of -1.5<[Fe/H]<= -0.5, the thick disk
stars show constantly high mean [Mg/Fe] and [Si/Fe] ratios with small scatter.
In contrast, the inner, and the outer halo stars show lower mean values of
these abundance ratios with larger scatter. The [Mg/Fe], [Si/Fe] and [Ca/Fe]
for the inner and the outer halo stars also show weak decreasing trends with
[Fe/H] in the range [Fe/H]. These results favor the scenarios that the MW
thick disk formed through rapid chemical enrichment primarily through Type II
supernovae of massive stars, while the stellar halo has formed at least in part
via accretion of progenitor stellar systems having been chemically enriched
with different timescales.Comment: Accepted for publication in Ap
Properties of hadron and quark matter studied with a molecular dynamics
We study the hadron-quark phase transition in a molecular dynamics (MD) of
quark degrees of freedom. The hadron state at low density and temperature, and
the deconfined quark state at high density and temperature are observed in our
model. We investigate the equations of state and draw the phase-diagram at wide
baryon density and temperature range. We also discuss the transport property,
e.g. viscosity, of matter. It is found that the ratio of the shear
viscosity to the entropy density is less than one for quark matter.Comment: Poster presentation at Quark Matter 200
Kaon Condensation and the Non-Uniform Nuclear Matter
Non-uniform structures of nuclear matter are studied in a wide density-range.
Using the density functional theory with a relativistic mean-field model, we
examine non-uniform structures at sub-nuclear densities (nuclear ``pastas'')
and at high densities, where kaon condensate is expected. We try to give a
unified view about the change of the matter structure as density increases,
carefully taking into account the Coulomb screening effects from the viewpoint
of first-order phase transition.Comment: Presented at "Tours Symposium on Nuclear Physics V
Coulomb screening effect on the nuclear-pasta structure
Using the density functional theory (DFT) with the relativistic mean field
(RMF) model, we study the non-uniform state of nuclear matter, ``nuclear
pasta''. We self-consistently include the Coulomb interaction together with
other interactions. It is found that the Coulomb screening effect is
significant for each pasta structure but not for the bulk equation of state
(EOS) of the nuclear pasta phase
Mott Relation for Anomalous Hall and Nernst effects in Ga1-xMnxAs Ferromagnetic Semiconductors
The Mott relation between the electrical and thermoelectric transport
coefficients normally holds for phenomena involving scattering. However, the
anomalous Hall effect (AHE) in ferromagnets may arise from intrinsic spin-orbit
interaction. In this work, we have simultaneously measured AHE and the
anomalous Nernst effect (ANE) in Ga1-xMnxAs ferromagnetic semiconductor films,
and observed an exceptionally large ANE at zero magnetic field. We further show
that AHE and ANE share a common origin and demonstrate the validity of the Mott
relation for the anomalous transport phenomena
Fast Quasi-Threshold Editing
We introduce Quasi-Threshold Mover (QTM), an algorithm to solve the
quasi-threshold (also called trivially perfect) graph editing problem with edge
insertion and deletion. Given a graph it computes a quasi-threshold graph which
is close in terms of edit count. This edit problem is NP-hard. We present an
extensive experimental study, in which we show that QTM is the first algorithm
that is able to scale to large real-world graphs in practice. As a side result
we further present a simple linear-time algorithm for the quasi-threshold
recognition problem.Comment: 26 pages, 4 figures, submitted to ESA 201
Quasi-reversible Magnetoresistance in Exchange Spring Tunnel Junctions
We report a large, quasi-reversible tunnel magnetoresistance in
exchange-biased ferromagnetic semiconductor tunnel junctions wherein a soft
ferromagnetic semiconductor (\gma) is exchange coupled to a hard ferromagnetic
metal (MnAs). Our observations are consistent with the formation of a region of
inhomogeneous magnetization (an "exchange spring") within the biased \gma
layer. The distinctive tunneling anisotropic magnetoresistance of \gma produces
a pronounced sensitivity of the magnetoresistance to the state of the exchange
spring
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