3,225 research outputs found
Chorionic gonadotrophin regulates CXCR4 expression in human endometrium via E-series prostanoid receptor 2 signalling to PI3K-ERK1/2:Implications for fetal-maternal crosstalk for embryo implantation
Chemical abundances and kinematics of barium stars
In this paper we present an homogeneous analysis of photospheric abundances
based on high-resolution spectroscopy of a sample of 182 barium stars and
candidates. We determined atmospheric parameters, spectroscopic distances,
stellar masses, ages, luminosities and scale height, radial velocities,
abundances of the Na, Al, -elements, iron-peak elements, and s-process
elements Y, Zr, La, Ce, and Nd. We employed the local-thermodynamic-equilibrium
model atmospheres of Kurucz and the spectral analysis code {\sc moog}. We found
that the metallicities, the temperatures and the surface gravities for barium
stars can not be represented by a single gaussian distribution. The abundances
of -elements and iron peak elements are similar to those of field giants
with the same metallicity. Sodium presents some degree of enrichment in more
evolved stars that could be attributed to the NeNa cycle. As expected, the
barium stars show overabundance of the elements created by the s-process. By
measuring the mean heavy-element abundance pattern as given by the ratio
[s/Fe], we found that the barium stars present several degrees of enrichment.
We also obtained the [hs/ls] ratio by measuring the photospheric abundances of
the Ba-peak and the Zr-peak elements. Our results indicated that the [s/Fe] and
the [hs/ls] ratios are strongly anti-correlated with the metallicity. Our
kinematical analysis showed that 90% of the barium stars belong to the thin
disk population. Based on their luminosities, none of the barium stars are
luminous enough to be an AGB star, nor to become self-enriched in the s-process
elements. Finally, we determined that the barium stars also follow an
age-metallicity relation.Comment: 30 pages, 26 figures, 18 tables, accepted for publication in MNRA
Complex itinerant ferromagnetism in noncentrosymmetric Cr11Ge19
The noncentrosymmetric ferromagnet Cr11Ge19 has been investigated by
electrical transport, AC and DC magnetization, heat capacity, x-ray
diffraction, resonant ultrasound spectroscopy, and first principles electronic
structure calculations. Complex itinerant ferromagnetism in this material is
indicated by nonlinearity in conventional Arrott plots, unusual behavior of AC
susceptibility, and a weak heat capacity anomaly near the Curie temperature (88
K). The inclusion of spin wave excitations was found to be important in
modeling the low temperature heat capacity. The temperature dependence of the
elastic moduli and lattice constants, including negative thermal expansion
along the c axis at low temperatures, indicate strong magneto-elastic coupling
in this system. Calculations show strong evidence for itinerant ferromagnetism
and suggest a noncollinear ground state may be expected
Scaling approach to order-parameter fluctuations in disordered frustrated systems
We present a constructive approach to obtain information about the
compactness and shape of large-scale lowest excitations in disordered systems
by studying order-parameter fluctuations (OPF) at low temperatures. We show
that the parameter which measures OPF is 1/3 at T=0 provided the ground
state is unique and the probability distribution for the lowest excitations is
gapless and with finite weight at zero-excitation energy. We then apply
zero-temperature scaling to describe the energy and volume spectra of the
lowest large-scale excitations which scale with the system size and have a
weight at ze ro energy with . A
low-temperature expansion reveals that, OPF vanish like , if
and remain finite for space filling lowest excitations with
. The method can be extended to extract information about the shape
and fractal surface of the large-scale lowest excitations.Comment: 4 pages, REVTeX. Some modifications; final version accepted for
publication in J. Phys. A: Math. and General (Letters
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