1,279 research outputs found
Asteroseismology across the HR diagram
High precision spectroscopy provides essential information necessary to fully
exploit the opportunity of probing the internal structure of stars using
Asteroseismology. In this work we discuss how Asteroseismology combined with
High Precision Spectroscopy can establish a detailed view on stellar structure
and evolution of stars across the HR diagramme.Comment: 6 pages, 2 figures - to appear in Precision Spectroscopy in
Astrophysics, (Eds) L. Pasquini, M. Romaniello, N.C. Santos, and A. Correia,
ESO Astrophysics Symposia, 200
Symmetry of the order parameter in superconducting ZrZn_2
We apply symmetry considerations to study the possible superconducting order
parameters in ferromagnetic ZrZn_2. We predict that the presence and the
location of the superconducting gap nodes depend on the direction of
magnetization M. In particular, if M is directed along the z axis, then the
order parameter should always have zeros. We also discuss how to determine the
gap symmetry in ZrZn_2 using ultrasound attenuation measurements.Comment: 6 pages, submitted to PRB; some corrections and discussion adde
Order parameter symmetry in ferromagnetic superconductors
We analyze the symmetry and the nodal structure of the superconducting order
parameter in a cubic ferromagnet, such as ZrZn. We demonstrate how the
order parameter symmetry evolves when the electromagnetic interaction of the
conduction electrons with the internal magnetic induction and the spin-orbit
coupling are taken into account. These interactions break the cubic symmetry
and lift the degeneracy of the order parameter. It is shown that the order
parameter which appears immediately below the critical temperature has two
components, and its symmetry is described by {\em co-representations} of the
magnetic point groups. This allows us to make predictions about the location of
the gap nodes.Comment: 12 pages, ReVTeX, submitted to PR
Bulk Scale Factor at Very Early Universe
In this paper we propose a higher dimensional Cosmology based on FRW model
and brane-world scenario. We consider the warp factor in the brane-world
scenario as a scale factor in 5-dimensional generalized FRW metric, which is
called as bulk scale factor, and obtain the evolution of it with space-like and
time-like extra dimensions. It is then showed that, additional space-like
dimensions can produce exponentially bulk scale factor under repulsive strong
gravitational force in the empty universe at a very early stage.Comment: 7 pages, October 201
Non-magnetic impurity scattering in a superconductor near a van Hove point: Zn versus Ni in the cuprates
We consider the effect of non-magnetic impurities in a
superconductor with \ef close to a van Hove singularity. It is shown that the
non-trivial density of states (DOS) allows for resonant scattering already at
intermediate potential strengths eV. The residual DOS at
\ef, and the \tc suppression rate are found to strongly depend on the carrier
concentration. Quantitative agreement with experiments on Zn and Ni doped
cuprates is obtained by adjusting a single parameter, .Comment: 4 pages uuencoded compressed Postscript (Minor changes
On velocity-dependent dark matter annihilations in dwarf satellites
Milky Way dwarf spheroidal satellites are a prime target for Dark Matter (DM) indirect searches. Recently the importance of possible long-range interactions has been recognized, as they can boost the expected DM gamma ray signal by orders of magnitude through an effect commonly known as the Sommerfeld enhancement. However, for such analyses precise modelling of DM phase-space distribution becomes crucial and can introduce large uncertainties in the final result. We provide a pioneering attempt towards a comprehensive investigation of these systematics. First, the DM halo profiles are constrained using Bayesian inference on the available stellar kinematic datasets with a careful treatment of observational and theoretical uncertainties. We consider both cuspy and cored parametric DM density profiles, together with the case of a non-parametric halo modelling directly connected to observable quantities along the line-of-sight. After reconsidering the study case of ergodic systems, the basic ingredient of all previous analyses, we investigate for the first time scenarios where DM particles are allowed to have anisotropic velocity distributions. Referring to a generalized J-factor, sensitive to velocity-dependent effects, an enhancement (suppression) with respect to the isotropic phase-space distributions is obtained for the case of tangentially (radially) biased DM particle orbits. We provide new estimates for J-factors for the eight brightest Milky Way dwarfs also in the limit of velocity-independent DM annihilation, in good agreement with previous results in literature, and derive data-driven lower-bounds based on the non-parametric modelling of the halo density. This work presents a state-of-the-art analysis of the aforementioned effects and falls within the interest of current and future experimental collaborations involved in DM indirect detection programs
Sum rule for the backward spin polarizability of the nucleon from a backward dispersion relation
A new sum rule for , the backward spin polarizability of the
nucleon, is derived from a backward-angle dispersion relation. Taking into
account single- and multi-pion photoproduction in the s-channel up to the
energy 1.5 GeV and resonances in the t-channel with mass below 1.5 GeV, it is
found for the proton and neutron that = -39.5 +/- 2.4 and
= 52.5 +/- 2.4, respectively, in units of 10^{-4} fm^4.Comment: 10 pages, 1 figure, revtex. Submitted to Phys. Lett.
Wide Angle Polarization Analysis with Neutron Spin Filters
AbstractWe report substantial improvements in a compact wide angle neutron spin filter system that was recently employed on the Multi- Axis Crystal Spectrometer at the Center for Neutron Research at the U.S. National Institute of Standards and Technology. The apparatus consists of a cylindrical 3He polarizer cell and wide-angle 3He analyzer cells, a vertical solenoid to provide a uniform magnetic field, and a shielded radio-frequency solenoid for the polarizer cell. Nuclear magnetic resonance is employed to reverse the polarization in the polarizer cell and monitor the 3He polarization in all cells. The first experiment using this apparatus was carried out with cylindrical analyzer cells with limited angular coverage due to low polarizations in fused quartz cells. We present results for aluminosilicate glass analyzer cells that cover 110 ∘ and have long relaxation times (100h to 400h). Using two 100W diode bars spectrally narrowed with chirped volume Bragg gratings, we have obtained 65% - 80% 3He polarization in these cells. The 3He polarization has been measured by neutron transmission and electron paramagnetic resonance. Additional progress includes an improved holding field solenoid and decreased spin-flip losses
Height and risk of death among men and women: aetiological implications of associations with cardiorespiratory disease and cancer mortality
OBJECTIVES: Height is inversely associated with cardiovascular disease mortality risk and has shown variable associations with cancer incidence and mortality. The interpretation of findings from previous studies has been constrained by data limitations. Associations between height and specific causes of death were investigated in a large general population cohort of men and women from the West of Scotland.
DESIGN: Prospective observational study.
SETTING: Renfrew and Paisley, in the West of Scotland.
SUBJECTS: 7052 men and 8354 women aged 45-64 were recruited into a study in Renfrew and Paisley, in the West of Scotland, between 1972 and 1976. Detailed assessments of cardiovascular disease risk factors, morbidity and socioeconomic circumstances were made at baseline.
MAIN OUTCOME MEASURES: Deaths during 20 years of follow up classified into specific causes.
RESULTS: Over the follow up period 3347 men and 2638 women died. Height is inversely associated with all cause, coronary heart disease, stroke, and respiratory disease mortality among men and women. Adjustment for socioeconomic position and cardiovascular risk factors had little influence on these associations. Height is strongly associated with forced expiratory volume in one second (FEV1) and adjustment for FEV1 considerably attenuated the association between height and cardiorespiratory mortality. Smoking related cancer mortality is not associated with height. The risk of deaths from cancer unrelated to smoking tended to increase with height, particularly for haematopoietic, colorectal and prostate cancers. Stomach cancer mortality was inversely associated with height. Adjustment for socioeconomic position had little influence on these associations.
CONCLUSION: Height serves partly as an indicator of socioeconomic circumstances and nutritional status in childhood and this may underlie the inverse associations between height and adulthood cardiorespiratory mortality. Much of the association between height and cardiorespiratory mortality was accounted for by lung function, which is also partly determined by exposures acting in childhood. The inverse association between height and stomach cancer mortality probably reflects Helicobacter pylori infection in childhood resulting inor being associated withshorter height. The positive associations between height and several cancers unrelated to smoking could reflect the influence of calorie intake during childhood on the risk of these cancers
Prospects for asteroseismology
The observational basis for asteroseismology is being dramatically
strengthened, through more than two years of data from the CoRoT satellite, the
flood of data coming from the Kepler mission and, in the slightly longer term,
from dedicated ground-based facilities. Our ability to utilize these data
depends on further development of techniques for basic data analysis, as well
as on an improved understanding of the relation between the observed
frequencies and the underlying properties of the stars. Also, stellar modelling
must be further developed, to match the increasing diagnostic potential of the
data. Here we discuss some aspects of data interpretation and modelling,
focussing on the important case of stars with solar-like oscillations.Comment: Proc. HELAS Workshop on 'Synergies between solar and stellar
modelling', eds M. Marconi, D. Cardini & M. P. Di Mauro, Astrophys. Space
Sci., in the press Revision: correcting abscissa labels on Figs 1 and
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