654 research outputs found
Simulation of Transitions between "Pasta" Phases in Dense Matter
Calculations of equilibrium properties of dense matter predict that at
subnuclear densities nuclei can be rodlike or slablike. To investigate whether
transitions between phases with non-spherical nuclei can occur during the
collapse of a star, we perform quantum molecular dynamic simulations of the
compression of dense matter. We have succeeded in simulating the transitions
between rodlike and slablike nuclei and between slablike nuclei and cylindrical
bubbles. Our results strongly suggest that non-spherical nuclei can be formed
in the inner cores of collapsing stars.Comment: 4 pages, 4 figures, final version published in Phys. Rev. Lett.,
high-res figures can be seen at http://www.nordita.dk/~gentaro/research/fig
Blood levels of the micronutrient zinc decrease with advancing age in normally nourished elderly persons
Roles of Supernova Ejecta in Nucleosynthesis of Light Elements, Li, Be, and B
Explosions of type Ic supernovae (SNe Ic) are investigated using a
relativistic hydrodynamic code to study roles of their outermost layers of the
ejecta in light element nucleosynthesis through spallation reactions as a
possible mechanism of the "primary" process. We have confirmed that the energy
distribution of the outermost layers with a mass fraction of only 0.001 %
follows the empirical formula proposed by previous work when the explosion is
furious. In such explosions, a significant fraction of the ejecta (0.1 % in
mass) have the energy greater than the threshold energy for spallation
reactions. On the other hand, it is found that the outermost layers of ejecta
become more energetic than the empirical formula would predict when the
explosion energy per unit ejecta mass is smaller than \sim 1.3\times
10^{51}{ergs/}\Msun. As a consequence, it is necessary to numerically
calculate explosions to estimate light element yields from SNe Ic. The usage of
the empirical formula would overestimate the yields by a factor of \gtsim 3
for energetic explosions such as SN 1998bw and underestimate the yields by a
similar factor for less energetic explosions like SN 1994I. The yields of light
elements Li, Be, and B (LiBeB) from SNe Ic are estimated by solving the
transfer equation of cosmic rays originated from ejecta of SNe Ic and compared
with observations.Comment: 10 pages, 6 figures, 2 tables, to appear in The Astrophysical Journa
Microscopic Study of Slablike and Rodlike Nuclei: Quantum Molecular Dynamics Approach
Structure of cold dense matter at subnuclear densities is investigated by
quantum molecular dynamics (QMD) simulations. We succeeded in showing that the
phases with slab-like and rod-like nuclei etc. can be formed dynamically from
hot uniform nuclear matter without any assumptions on nuclear shape. We also
observe intermediate phases, which has complicated nuclear shapes. Geometrical
structures of matter are analyzed with Minkowski functionals, and it is found
out that intermediate phases can be characterized as ones with negative Euler
characteristic. Our result suggests the existence of these kinds of phases in
addition to the simple ``pasta'' phases in neutron star crusts.Comment: 6 pages, 4 figures, RevTex4; to be published in Phys. Rev. C Rapid
Communication (accepted version
Algorithm for Linear Response Functions at Finite Temperatures: Application to ESR spectrum of s=1/2 Antiferromagnet Cu benzoate
We introduce an efficient and numerically stable method for calculating
linear response functions of quantum systems at finite
temperatures. The method is a combination of numerical solution of the
time-dependent Schroedinger equation, random vector representation of trace,
and Chebyshev polynomial expansion of Boltzmann operator. This method should be
very useful for a wide range of strongly correlated quantum systems at finite
temperatures. We present an application to the ESR spectrum of s=1/2
antiferromagnet Cu benzoate.Comment: 4 pages, 4 figure
Probing a ferromagnetic critical regime using nonlinear susceptibility
The second order para-ferromagnetic phase transition in a series of amorphous
alloys (Fe{_5}Co{_{50}}Ni{_{17-x}}Cr{_x}B{_{16}}Si{_{12}}) is investigated
using nonlinear susceptibility. A simple molecular field treatment for the
critical region shows that the third order suceptibility (chi{_3}) diverges on
both sides of the transition temperature, and changes sign at T{_C}. This
critical behaviour is observed experimentally in this series of amorphous
ferromagnets, and the related assymptotic critical exponents are calculated. It
is shown that using the proper scaling equations, all the exponents necessary
for a complete characterization of the phase transition can be determined using
linear and nonlinear susceptiblity measurements alone. Using meticulous
nonlinear susceptibility measurements, it is shown that at times chi{_3} can be
more sensitive than the linear susceptibility (chi{_1}) in unravelling the
magnetism of ferromagnetic spin systems. A new technique for accurately
determining T{_C} is discussed, which makes use of the functional form of
chi{_3} in the critical region.Comment: 11 Figures, Submitted to Physical Review
KLF11 and association study in Japanese
Aims: KrĂźppel-like factor 11 (KLF11) is a transcriptional factor of the zinc finger domain family that regulates the expression of insulin. In North European populations, its common functional variant Q62R (rs35927125) is a strong genetic factor for Type 2 diabetes (P = 0.00033, odds ratio for G allele = 1.29, 95% CI 1.12â1.49). We examined the contribution of KLF11 variants to the susceptibility to Type 2 diabetes in a Japanese population.
Methods: By re-sequencing Japanese individuals (n = 24, partly 96), we screened all four exons, exon/intron boundaries and flanking regions of KLF11. Verified single nucleotide polymorphisms (SNPs) were genotyped in 731 initial samples (369 control and 362 case subjects). Subsequently, we tested for association in 1087 samples (524 control and 563 case subjects), which were collected in different districts of Japan from the initial samples.
Results: We identified eight variants, including a novel A/C variant on intron 3, but no mis-sense mutations. In an association study, we failed to find any significant result of SNPs (minor allele frequency 8.2â46.2%) after correcting for multiple testing. Similarly, no haplotypes were associated with Type 2 diabetes. It is notable that the G allele in rs35927125 was completely absent in 1818 Japanese individuals.
Conclusions: Genetic variants in KLF11 are unlikely to have a major effect of Type 2 diabetes in the Japanese population, although they were significantly associated in North European populations. These observations might help to determine the role of KLF11 variants in Type 2 diabetes in different populations
Accretion of dust grains as a possible origin of metal-poor stars with low alpha/Fe ratios
The origin of low alpha/Fe ratios in some metal-poor stars, so called
low-alpha stars, is discussed. It is found that most of low-alpha stars in the
Galaxy are on the main-sequence. This strongly suggests that these stars
suffered from external pollution. It is also found that the abundance ratios
Zn/Fe of low-alpha stars both in the Galaxy and in dwarf spheroidal galaxies
are lower than the average value of Galactic halo stars whereas damped Ly alpha
absorbers have higher ratios. This implies that some low-alpha stars accreted
matter depleted from gas onto dust grains. To explain the features in these
low-alpha stars, we have proposed that metal-poor stars harboring planetary
systems are the origin of these low-alpha stars. Stars engulfing a small
fraction of planetesimals enhance the surface content of Fe to exhibit low
alpha/Fe ratios on their surfaces while they are on the main-sequence, because
dwarfs have shallow surface convection zones where the engulfed matter is
mixed. After the stars leave the main-sequence, the surface convection zones
become deeper to reduce the enhancement of Fe. Eventually, when the stars
ascend to the tip of the red giant branch, they engulf giant planets to become
low-alpha stars again as observed in dwarf spheroidal galaxies. We predict that
low-alpha stars with low Mn/Fe ratios harbor planetary systems.Comment: 6 pages, 4 figures, accepted for publication in The Astrophysical
Journal Letters, references correcte
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