11,841 research outputs found
Critical Analysis of Baryon Masses and Sigma-Terms in Heavy Baryon Chiral Perturbation Theory
We present an analysis of the octet baryon masses and the and
--terms in the framework of heavy baryon chiral perturbation theory. At
next-to-leading order, , knowledge of the baryon masses and
allows to determine the three corresponding finite
low--energy constants and to predict the the two --terms
. We also include the spin-3/2 decuplet in the
effective theory. The presence of the non--vanishing energy scale due to the
octet--decuplet splitting shifts the average octet baryon mass by an infinite
amount and leads to infinite renormalizations of the low--energy constants. The
first observable effect of the decuplet intermediate states to the baryon
masses starts out at order . We argue that it is not sufficient to retain
only these but no other higher order terms to achieve a consistent description
of the three--flavor scalar sector of baryon CHPT. In addition, we critically
discuss an SU(2) result which allows to explain the large shift of via intermediate states.Comment: 18 pp, TeX, BUTP-93/05 and CRN-93-0
Electromagnetic Moments of the Baryon Decuplet
We compute the leading contributions to the magnetic dipole and electric
quadrupole moments of the baryon decuplet in chiral perturbation theory. The
measured value for the magnetic moment of the is used to determine
the local counterterm for the magnetic moments. We compare the chiral
perturbation theory predictions for the magnetic moments of the decuplet with
those of the baryon octet and find reasonable agreement with the predictions of
the large-- limit of QCD. The leading contribution to the quadrupole
moment of the and other members of the decuplet comes from one--loop
graphs. The pionic contribution is shown to be proportional to (and so
will not contribute to the quadrupole moment of nuclei), while the
contribution from kaons has both isovector and isoscalar components. The chiral
logarithmic enhancement of both pion and kaon loops has a coefficient that
vanishes in the limit. The third allowed moment, the magnetic octupole,
is shown to be dominated by a local counterterm with corrections arising at two
loops. We briefly mention the strange counterparts of these moments.Comment: Uses harvmac.tex, 15 pages with 3 PostScript figures packed using
uufiles. UCSD/PTH 93-22, QUSTH-93-05, Duke-TH-93-5
Chiral Perturbation Theory for , , and
We use heavy vector meson chiral perturbation theory
to predict differential decay distributions for and in the kinematic region where
(here or ) is much smaller than the
chiral symmetry breaking scale. Using the large number of colors limit we also
predict the rate for in this region (now
). Comparing our prediction with experimental data, we determine
one of the coupling constants in the heavy vector meson chiral Lagrangian.Comment: 14 pages, latex 2e. We include the decay of the tau into the omega,
pi minus and the tau neutrino, and extract a value for the coupling constant
g2, using experimental dat
SPECIES II. Stellar parameters of the EXPRESS program giant star sample
As part of the search for planets around evolved stars, we can understand
planet populations around significantly higher-mass stars than the Sun on the
main sequence. This population is difficult to study any other way,
particularly with radial-velocities since these stars are too hot and rotate
too fast to measure precise velocities. Here we estimate stellar parameters for
all of the giant stars from the EXPRESS project, which aims to detect planets
orbiting evolved stars, and study their occurrence rate as a function of
stellar mass. We analyse high resolution echelle spectra of these stars, and
compute the atmospheric parameters by measuring the equivalent widths for a set
of iron lines, using an updated method implemented during this work. Physical
parameters are computed by interpolating through a grid of stellar evolutionary
models, following a procedure that carefully takes into account the post-MS
evolutionary phases. Probabilities of the star being in the red giant branch
(RBG) or the horizontal branch (HB) are estimated from the derived
distributions. Results: We find that, out of 166 evolved stars, 101 of them are
most likely in the RGB phase, while 65 of them are in the HB phase. The mean
derived mass is 1.41 and 1.87 Msun for RGB and HB stars, respectively. To
validate our method, we compared our results with interferometry and
asteroseismology studies. We find a difference in the radius with
interferometry of 1.7%. With asteroseismology, we find 2.4% difference in logg,
1.5% in radius, 6.2% in mass, and 11.9% in age. Compared with previous
spectroscopic studies, and find a 0.5% difference in Teff, 1% in logg, and 2%
in [Fe/H]. We also find a mean mass difference with respect to the EXPRESS
original catalogue of 16%. We show that the method presented here can greatly
improve the estimates of the stellar parameters for giant stars compared to
what was presented previously.Comment: 24 pages, 17 figures, 15 tables, accepted by A&
Exotic magnetism in the alkali sesquoxides Rb4O6 and Cs4O6
Among the various alkali oxides the sesquioxides Rb4O6 and Cs4O6 are of
special interest. Electronic structure calculations using the local
spin-density approximation predicted that Rb4O6 should be a half-metallic
ferromagnet, which was later contradicted when an experimental investigation of
the temperature dependent magnetization of Rb4O6 showed a low-temperature
magnetic transition and differences between zero-field-cooled (ZFC) and
field-cooled (FC) measurements. Such behavior is known from spin glasses and
frustrated systems. Rb4O6 and Cs4O6 comprise two different types of dioxygen
anions, the hyperoxide and the peroxide anions. The nonmagnetic peroxide anions
do not contain unpaired electrons while the hyperoxide anions contain unpaired
electrons in antibonding pi*-orbitals. High electron localization (narrow
bands) suggests that electronic correlations are of major importance in these
open shell p-electron systems. Correlations and charge ordering due to the
mixed valency render p-electron-based anionogenic magnetic order possible in
the sesquioxides. In this work we present an experimental comparison of Rb4O6
and the related Cs4O6. The crystal structures are verified using powder x-ray
diffraction. The mixed valency of both compounds is confirmed using Raman
spectroscopy, and time-dependent magnetization experiments indicate that both
compounds show magnetic frustration, a feature only previously known from d-
and f-electron systems
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Women's views of continuity of information provided during and after pregnancy: A qualitative interview study
Straightforward transfer of care from pregnancy to the postpartum period is associated with health benefits and is desired by women worldwide. Underpinning this transfer of care is the sharing of information between healthcare professionals and the provision of consistent information to women. In this qualitative study, two aspects of continuity of information were examined; first the information passed on from midwife to health visitor regarding a woman and her baby before the health visitor meets the woman postnatally and second, the consistency of information received by women from these two healthcare professionals (the main healthcare providers during and after pregnancy in England). To be eligible for the study, women had to have had a baby in England within 12 months prior to the interview. Participants also needed to be able to read and speak English and be over 18 years old. Recruitment of participants was via word of mouth and social media. Twenty-nine mothers were interviewed of whom 19 were first time mothers. The interviews took place in the summer and autumn of 2016 and were transcribed verbatim and analysed using Framework Analysis. Two overarching themes were identified: not feeling listened to and information inconsistencies. Women reported little experience of midwives and health visitors sharing information about their care, forcing women to repeat information. This made women feel not listened to and participants recommended that healthcare professionals share information; prioritising information about labour, mental health, and chronic conditions. Women had mixed experiences regarding receiving information from midwives and health visitors, with examples of both consistent and inconsistent information received. To avoid inconsistent information, joint appointments were recommended. Findings from this study clearly suggest that better communication pathways need to be developed and effectively implemented for midwives and health visitors to improve the care that they provide to women
Velocity Statistics in the Two-Dimensional Granular Turbulence
We studied the macroscopic statistical properties on the freely evolving
quasi-elastic hard disk (granular) system by performing a large-scale (up to a
few million particles) event-driven molecular dynamics systematically and found
that remarkably analogous to an enstrophy cascade process in the decaying
two-dimensional fluid turbulence. There are four typical stages in the freely
evolving inelastic hard disk system, which are homogeneous, shearing (vortex),
clustering and final state. In the shearing stage, the self-organized
macroscopic coherent vortices become dominant. In the clustering stage, the
energy spectra are close to the expectation of Kraichnan-Batchelor theory and
the squared two-particle separation strictly obeys Richardson law.Comment: 4 pages, 4 figures, to be published in PR
Attempted density blowup in a freely cooling dilute granular gas: hydrodynamics versus molecular dynamics
It has been recently shown (Fouxon et al. 2007) that, in the framework of
ideal granular hydrodynamics (IGHD), an initially smooth hydrodynamic flow of a
granular gas can produce an infinite gas density in a finite time. Exact
solutions that exhibit this property have been derived. Close to the
singularity, the granular gas pressure is finite and almost constant. This work
reports molecular dynamics (MD) simulations of a freely cooling gas of nearly
elastically colliding hard disks, aimed at identifying the "attempted" density
blowup regime. The initial conditions of the simulated flow mimic those of one
particular solution of the IGHD equations that exhibits the density blowup. We
measure the hydrodynamic fields in the MD simulations and compare them with
predictions from the ideal theory. We find a remarkable quantitative agreement
between the two over an extended time interval, proving the existence of the
attempted blowup regime. As the attempted singularity is approached, the
hydrodynamic fields, as observed in the MD simulations, deviate from the
predictions of the ideal solution. To investigate the mechanism of breakdown of
the ideal theory near the singularity, we extend the hydrodynamic theory by
accounting separately for the gradient-dependent transport and for finite
density corrections.Comment: 11 pages, 9 figures, accepted for publication on Physical Review
Imaging the essential role of spin-fluctuations in high-Tc superconductivity
We have used scanning tunneling spectroscopy to investigate short-length
electronic correlations in three-layer Bi2Sr2Ca2Cu3O(10+d) (Bi-2223). We show
that the superconducting gap and the energy Omega_dip, defined as the
difference between the dip minimum and the gap, are both modulated in space
following the lattice superstructure, and are locally anti-correlated. Based on
fits of our data to a microscopic strong-coupling model we show that Omega_dip
is an accurate measure of the collective mode energy in Bi-2223. We conclude
that the collective mode responsible for the dip is a local excitation with a
doping dependent energy, and is most likely the (pi,pi) spin resonance.Comment: 4 pages, 4 figure
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