8,422 research outputs found
Masses, Oxygen and Carbon abundances in CHEPS dwarf stars
Reproduced with permission from Astronomy & Astrophysics. © 2019 ESOContext. We report the results from the determination of stellar masses, carbon, and oxygen abundances in the atmospheres of 107 stars from the Calan-Hertfordshire Extrasolar Planet Search (CHEPS) programme. Our stars are drawn from a population with a significantly super-solar metallicity. At least 10 of these stars are known to host orbiting planets. Aims. In this work, we set out to understand the behaviour of carbon and oxygen abundance in stars with different spectral classes, metallicities, and V sin i within the metal-rich stellar population. Methods. Masses of these stars were determined using data from Gaia DR2. Oxygen and carbon abundances were determined by fitting the absorption lines. We determined oxygen abundances with fits to the 6300.304 Å O I line, and we used 3 lines of the C I atom and 12 lines of the C 2 molecule for the determination of carbon abundances. Results. We determine masses and abundances of 107 CHEPS stars. There is no evidence that the [C/O] ratio depends on V sin i or the mass of the star within our constrained range of masses, i.e. 0.82 5 km s -1) are massive stars.Peer reviewedFinal Published versio
Hyperon Nonleptonic Decays in Chiral Perturbation Theory Reexamined
We recalculate the leading nonanalytic contributions to the amplitudes for
hyperon nonleptonic decays in chiral perturbation theory. Our results partially
disagree with those calculated before, and include new terms previously omitted
in the P-wave amplitudes. Although these modifications are numerically
significant, they do not change the well-known fact that good agreement with
experiment cannot be simultaneously achieved using one-loop S- and P-wave
amplitudes.Comment: 14 pages, latex, 3 figures, uses axodraw.sty, minor additions, to
appear in Phys. Rev.
Shocks in supersonic sand
We measure time-averaged velocity, density, and temperature fields for steady
granular flow past a wedge and calculate a speed of granular pressure
disturbances (sound speed) equal to 10% of the flow speed. The flow is
supersonic, forming shocks nearly identical to those in a supersonic gas.
Molecular dynamics simulations of Newton's laws and Monte Carlo simulations of
the Boltzmann equation yield fields in quantitative agreement with experiment.
A numerical solution of Navier-Stokes-like equations agrees with a molecular
dynamics simulation for experimental conditions excluding wall friction.Comment: 4 pages, 5 figure
Dynamics and stress in gravity driven granular flow
We study, using simulations, the steady-state flow of dry sand driven by
gravity in two-dimensions. An investigation of the microscopic grain dynamics
reveals that grains remain separated but with a power-law distribution of
distances and times between collisions.
While there are large random grain velocities, many of these fluctuations are
correlated across the system and local rearrangements are very slow. Stresses
in the system are almost entirely transfered by collisions and the structure of
the stress tensor comes almost entirely from a bias in the directions in which
collisions occur.Comment: 4 pages, 3 eps figures, RevTe
Making sense of IL-6 signalling cues in pathophysiology
Unravelling the molecular mechanisms that account for functional pleiotropy is a major challenge for researchers in cytokine biology. Cytokine–receptor cross-reactivity and shared signalling pathways are considered primary drivers of cytokine pleiotropy. However, reports epitomized by studies of Jak-STAT cytokine signalling identify interesting biochemical and epigenetic determinants of transcription factor regulation that affect the delivery of signal-dependent cytokine responses. Here, a regulatory interplay between STAT transcription factors and their convergence to specific genomic enhancers support the fine-tuning of cytokine responses controlling host immunity, functional identity, and tissue homeostasis and repair. In this review, we provide an overview of the signalling networks that shape the way cells sense and interpret cytokine cues. With an emphasis on the biology of interleukin-6, we highlight the importance of these mechanisms to both physiological processes and pathophysiological outcomes
The Distribution of Nearby Stars in Velocity Space Inferred from Hipparcos Data
(abridged) The velocity distribution f(v) of nearby stars is estimated, via a
maximum- likelihood algorithm, from the positions and tangential velocities of
a kinematically unbiased sample of 14369 stars observed by the HIPPARCOS
satellite. f(v) shows rich structure in the radial and azimuthal motions, v_R
and v_phi, but not in the vertical velocity, v_z: there are four prominent and
many smaller maxima, many of which correspond to well known moving groups.
While samples of early-type stars are dominated by these maxima, also up to 25%
of red main-sequence stars are associated with them. These moving groups are
responsible for the vertex deviation measured even for samples of late-type
stars; they appear more frequently for ever redder samples; and as a whole they
follow an asymmetric-drift relation, in the sense that those only present in
red samples predominantly have large |v_R| and lag in v_phi w.r.t. the local
standard of rest (LSR). The question arise, how these old moving groups got on
their eccentric orbits. A plausible mechanism, known from solar system
dynamics, which is able to manage a shift in orbit space involves locking into
an orbital resonance.
Apart from these moving groups, there is a smooth background distribution,
akin to Schwarzschild's ellipsoidal model, with axis ratio of about 1:0.6:0.35
in v_R, v_phi, and v_z. The contours are aligned with the direction, but
not w.r.t. the v_phi and v_z axes: the mean v_z increases for stars rotating
faster than the LSR. This effect can be explained by the stellar warp of the
Galactic disk. If this explanation is correct, the warp's inner edge must not
be within the solar circle, while its pattern rotates with frequency of about
13 km/s/kpc or more retrograde w.r.t. the stellar orbits.Comment: 16 pages LaTeX (aas2pp4.sty), 6 figures, accepted by A
Radiative Neutron-Proton Capture in Effective Chiral Lagrangians
We calculate the cross-section for the thermal
process in chiral perturbation theory to next-to-next-to-leading order using
heavy-fermion formalism. The exchange current correction is found to be
in amplitude and the chiral perturbation at one-loop order
gives the cross section \sigma_{th}^{np}=(334\pm 2)\ {\mbox mb} which is in
agreement with the experimental value (334.2\pm 0.5)\ {\mbox mb}. Together
with the axial charge transitions, this provides a strong support for the power
of chiral Lagrangians for nuclear physics.Comment: 9 pages, revtex, uses epsfig.sty, 2 uuencoded figure
Energy levels of the soliton--heavy-meson bound states
We investigate the bound states of heavy mesons with finite masses to a
classical soliton solution in the Skyrme model. For a given model Lagrangian we
solve the equations of motion exactly so that the heavy vector mesons are
treated on the same footing as the heavy pseudoscalar mesons. All the energy
levels of higher grand spin states as well as the ground state are given over a
wide range of the heavy meson masses. We also examine the validity of the
approximations used in the literatures. The recoil effect of finite mass
soliton is naively estimated.Comment: 24 pages, REVTeX v3.0, 6 figures are available upon request
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