10,367 research outputs found
Comparison of the induction of pulmonary neoplasms in Sprague-Dawley rats by fission neutrons and radon daughters
Lung carcinomas in Sprague-Dawley rats after exposure to low doses of radon daughters, fission neutrons, or Îł-rays
M-dwarf stellar winds: the effects of realistic magnetic geometry on rotational evolution and planets
We perform three-dimensional numerical simulations of stellar winds of
early-M dwarf stars. Our simulations incorporate observationally reconstructed
large-scale surface magnetic maps, suggesting that the complexity of the
magnetic field can play an important role in the angular momentum evolution of
the star, possibly explaining the large distribution of periods in field dM
stars, as reported in recent works. In spite of the diversity of the magnetic
field topologies among the stars in our sample, we find that stellar wind
flowing near the (rotational) equatorial plane carries most of the stellar
angular momentum, but there is no preferred colatitude contributing to mass
loss, as the mass flux is maximum at different colatitudes for different stars.
We find that more non-axisymmetric magnetic fields result in more asymmetric
mass fluxes and wind total pressures (defined as the sum of
thermal, magnetic and ram pressures). Because planetary magnetospheric sizes
are set by pressure equilibrium between the planet's magnetic field and , variations of up to a factor of in (as found in the
case of a planet orbiting at several stellar radii away from the star) lead to
variations in magnetospheric radii of about 20 percent along the planetary
orbital path. In analogy to the flux of cosmic rays that impact the Earth,
which is inversely modulated with the non-axisymmetric component of the total
open solar magnetic flux, we conclude that planets orbiting M dwarf stars like
DT~Vir, DS~Leo and GJ~182, which have significant non-axisymmetric field
components, should be the more efficiently shielded from galactic cosmic rays,
even if the planets lack a protective thick atmosphere/large magnetosphere of
their own.Comment: 16 pages, 9 figures, to appear in MNRA
Preferred levels for background ducking to produce esthetically pleasing audio for TV with clear speech
In audio production, background ducking facilitates speech intelligibility while allowing the background to fulfill its purpose, e.g., to create ambience, set the mood, or convey semantic cues. Technical details for recommended ducking practices are not currently documented in the literature. Hence, we first analyzed common practices found in TV documentaries. Second, a listening test investigated the preferences of 22 normal-hearing participants on the Loud- ness Difference (LD) between commentary and background during ducking. Highly personal preferences were observed, highlighting the importance of object-based personalization. Sta- tistically significant difference was found between non-expert and expert listeners. On average, non-experts preferred LDs that were 4 LU higher than the ones preferred by experts. A sta- tistically significant difference was also found between Commentary over Music (CoM) and Commentary over Ambience (CoA). Based on the test results, we recommend at least 10 LU difference for CoM and at least 15 LU for CoA. Moreover, a computational method based on the Binaural Distortion-Weighted Glimpse Proportion (BiDWGP) was found to match the median preferred LD for each item with good accuracy (mean absolute error = 1.97 LU ± 2.50)
Modeling the RV jitter of early M dwarfs using tomographic imaging
In this paper we show how tomographic imaging (Zeeman Doppler Imaging, ZDI)
can be used to characterize stellar activity and magnetic field topologies,
ultimately allowing to filter out the radial velocity (RV) activity jitter of
M-dwarf moderate rotators. This work is based on spectropolarimetric
observations of a sample of five weakly-active early M-dwarfs (GJ 205, GJ 358,
GJ 410, GJ479, GJ 846) with HARPS-Pol and NARVAL. These stars have v sin i and
RV jitters in the range 1-2 km/s and 2.7-10.0 m/s rms respectively. Using a
modified version of ZDI applied to sets of phase-resolved Least-Squares- Decon-
volved (LSD) profiles of unpolarized spectral lines, we are able to
characterize the distribution of active regions at the stellar surfaces. We
find that darks spots cover less than 2% of the total surface of the stars of
our sample. Our technique is e cient at modeling the rotationally mod- ulated
component of the activity jitter, and succeeds at decreasing the amplitude of
this com- ponent by typical factors of 2-3 and up to 6 in optimal cases. From
the rotationally modulated time-series of circularly polarized spectra and with
ZDI, we also reconstruct the large-scale magnetic field topology. These fields
suggest that bi-stability of dynamo processes observed in active M dwarfs may
also be at work for moderately active M dwarfs. Comparing spot distributions
with field topologies suggest that dark spots causing activity jitter
concentrate at the magnetic pole and/or equator, to be confirmed with future
data on a larger sample.Comment: 34 pages, accepted for publication in MNRA
A homomorphism between link and XXZ modules over the periodic Temperley-Lieb algebra
We study finite loop models on a lattice wrapped around a cylinder. A section
of the cylinder has N sites. We use a family of link modules over the periodic
Temperley-Lieb algebra EPTL_N(\beta, \alpha) introduced by Martin and Saleur,
and Graham and Lehrer. These are labeled by the numbers of sites N and of
defects d, and extend the standard modules of the original Temperley-Lieb
algebra. Beside the defining parameters \beta=u^2+u^{-2} with u=e^{i\lambda/2}
(weight of contractible loops) and \alpha (weight of non-contractible loops),
this family also depends on a twist parameter v that keeps track of how the
defects wind around the cylinder. The transfer matrix T_N(\lambda, \nu) depends
on the anisotropy \nu and the spectral parameter \lambda that fixes the model.
(The thermodynamic limit of T_N is believed to describe a conformal field
theory of central charge c=1-6\lambda^2/(\pi(\lambda-\pi)).)
The family of periodic XXZ Hamiltonians is extended to depend on this new
parameter v and the relationship between this family and the loop models is
established. The Gram determinant for the natural bilinear form on these link
modules is shown to factorize in terms of an intertwiner i_N^d between these
link representations and the eigenspaces of S^z of the XXZ models. This map is
shown to be an isomorphism for generic values of u and v and the critical
curves in the plane of these parameters for which i_N^d fails to be an
isomorphism are given.Comment: Replacement of "The Gram matrix as a connection between periodic loop
models and XXZ Hamiltonians", 31 page
Quadrupolar Order in Isotropic Heisenberg Models with Biquadratic Interaction
Through Quantum Monte Carlo simulation, we study the biquadratic-interaction
model with the SU(2) symmetry in two and three dimensions. The zero-temperature
phase diagrams for the two cases are identical and exhibit an intermediate
phase characterized by finite quadrupole moment, in agreement with mean-field
type arguments and the semi-classical theory. In three dimensions, we
demonstrate that the model in the quadrupolar regime has a phase transition at
a finite temperature. In contrast to predictions by mean-field theories, the
phase transition to the quadrupolar phase turns out to be of the second order.
We also examine the critical behavior in the two marginal cases with the SU(3)
symmetry.Comment: 4 pages 5 figure
Complex magnetic topology and strong differential rotation on the low-mass T Tauri star V2247 Oph
From observations collected with the ESPaDOnS spectropolarimeter at the
Canada-France-Hawaii Telescope, we report the detection of Zeeman signatures on
the low-mass classical TTauri star (cTTS) V2247Oph. Profile distortions and
circular polarisation signatures detected in photospheric lines can be
interpreted as caused by cool spots and magnetic regions at the surface of the
star. The large-scale field is of moderate strength and highly complex;
moreover, both the spot distribution and the magnetic field show significant
variability on a timescale of only one week, as a likely result of strong
differential rotation. Both properties make V2247Oph very different from the
(more massive) prototypical cTTS BPTau; we speculate that this difference
reflects the lower mass of V2247Oph.
During our observations, V2247Oph was in a low-accretion state, with emission
lines showing only weak levels of circular polarisation; we nevertheless find
that excess emission apparently concentrates in a mid-latitude region of strong
radial field, suggesting that it is the footpoint of an accretion funnel.
The weaker and more complex field that we report on V2247Oph may share
similarities with those of very-low-mass late-M dwarfs and potentially explain
why low-mass cTTSs rotate on average faster than intermediate mass ones. These
surprising results need confirmation from new independent data sets on V2247Oph
and other similar low-mass cTTSs.Comment: MNRAS (in press) - 12 pages, 9 figure
A barata do coqueiro Coraliomela brunnea Thunb. (1981) (Coleoptera: Chrisomelidae).
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