601 research outputs found
On the magnetic field required for driving the observed angular-velocity variations in the solar convection zone
A putative temporally varying circulation-free magnetic-field configuration
is inferred in an equatorial segment of the solar convection zone from the
helioseismologically inferred angular-velocity variation, assuming that the
predominant dynamics is angular acceleration produced by the azimuthal Maxwell
stress exerted by a field whose surface values are consistent with photospheric
line-of-sight measurements.Comment: to appear in MNRA
Determining solar abundances using helioseismology
The recent downward revision of solar photospheric abundances of Oxygen and
other heavy elements has resulted in serious discrepancies between solar models
and solar structure as determined through helioseismology. In this work we
investigate the possibility of determining the solar heavy-element abundance
without reference to spectroscopy by using helioseismic data. Using the
dimensionless sound-speed derivative in the solar convection zone, we find that
the heavy element abundance, Z, of 0.0172 +/- 0.002, which is closer to the
older, higher value of the abundances.Comment: To appear in Ap
Temporal Variations in the Sun's Rotational Kinetic Energy
AIM: To study the variation of the angular momentum and the rotational
kinetic energy of the Sun, and associated variations in the gravitational
multipole moments, on a timescale of the solar cycle. METHOD: Inverting
helioseismic rotational splitting data obtained by the Global Oscillation
Network Group and by the Michelson Doppler Imager on the Solar and Heliospheric
Observatory. RESULTS: The temporal variation in angular momentum and kinetic
energy at high latitudes (>\pi/4) through the convection zone is positively
correlated with solar activity, whereas at low latitudes it is anticorrelated,
except for the top 10% by radius where both are correlated positively.
CONCLUSION: The helioseismic data imply significant temporal variation in the
angular momentum and the rotational kinetic energy, and in the gravitational
multipole moments. The properties of that variation will help constrain
dynamical theories of the solar cycle.Comment: To appear in Astronomy & Astrophysic
One-dimensional lattice of oscillators coupled through power-law interactions: Continuum limit and dynamics of spatial Fourier modes
We study synchronization in a system of phase-only oscillators residing on
the sites of a one-dimensional periodic lattice. The oscillators interact with
a strength that decays as a power law of the separation along the lattice
length and is normalized by a size-dependent constant. The exponent of
the power law is taken in the range . The oscillator frequency
distribution is symmetric about its mean (taken to be zero), and is
non-increasing on . In the continuum limit, the local density of
oscillators evolves in time following the continuity equation that expresses
the conservation of the number of oscillators of each frequency under the
dynamics. This equation admits as a stationary solution the unsynchronized
state uniform both in phase and over the space of the lattice. We perform a
linear stability analysis of this state to show that when it is unstable,
different spatial Fourier modes of fluctuations have different stability
thresholds beyond which they grow exponentially in time with rates that depend
on the Fourier modes. However, numerical simulations show that at long times,
all the non-zero Fourier modes decay in time, while only the zero Fourier mode
(i.e., the "mean-field" mode) grows in time, thereby dominating the instability
process and driving the system to a synchronized state. Our theoretical
analysis is supported by extensive numerical simulations.Comment: 7 pages, 4 figures. v2: new simulation results added, close to the
published versio
Experimental violation of a spin-1 Bell inequality using maximally-entangled four-photon states
We demonstrate the first experimental violation of a spin-1 Bell inequality.
The spin-1 inequality is a calculation based on the Clauser, Horne, Shimony and
Holt formalism. For entangled spin-1 particles the maximum quantum mechanical
prediction is 2.552 as opposed to a maximum of 2, predicted using local hidden
variables. We obtained an experimental value of 2.27 using the
four-photon state generated by pulsed, type-II, stimulated parametric
down-conversion. This is a violation of the spin-1 Bell inequality by more than
13 standard deviations.Comment: 5 pages, 3 figures, Revtex4. Problem with figures resolve
Experimental Falsification of Leggett's Non-Local Variable Model
Bell's theorem guarantees that no model based on local variables can
reproduce quantum correlations. Also some models based on non-local variables,
if subject to apparently "reasonable" constraints, may fail to reproduce
quantum physics. In this paper, we introduce a family of inequalities, which
allow testing Leggett's non-local model versus quantum physics, and which can
be tested in an experiment without additional assumptions. Our experimental
data falsify Leggett's model and are in agreement with quantum predictions.Comment: 5 pages, 3 figures, 1 tabl
Solar Cycle Related Changes at the Base of the Convection Zone
The frequencies of solar oscillations are known to change with solar
activity. We use Principal Component Analysis to examine these changes with
high precision. In addition to the well-documented changes in solar normal mode
oscillations with activity as a function of frequency, which originate in the
surface layers of the Sun, we find a small but statistically significant change
in frequencies with an origin at and below the base of the convection zone. We
find that at r=(0.712^{+0.0097}_{-0.0029})R_sun, the change in sound speed is
\delta c^2 / c^2 = (7.23 +/- 2.08) x 10^{-5} between high and low activity.
This change is very tightly correlated with solar activity. In addition, we use
the splitting coefficients to examine the latitudinal structure of these
changes. We find changes in sound speed correlated with surface activity for r
>~ 0.9R_sun.Comment: 29 pages, 11 figures, accepted for publication in Ap
Estimating stellar mean density through seismic inversions
Determining the mass of stars is crucial both to improving stellar evolution
theory and to characterising exoplanetary systems. Asteroseismology offers a
promising way to estimate stellar mean density. When combined with accurate
radii determinations, such as is expected from GAIA, this yields accurate
stellar masses. The main difficulty is finding the best way to extract the mean
density from a set of observed frequencies.
We seek to establish a new method for estimating stellar mean density, which
combines the simplicity of a scaling law while providing the accuracy of an
inversion technique.
We provide a framework in which to construct and evaluate kernel-based linear
inversions which yield directly the mean density of a star. We then describe
three different inversion techniques (SOLA and two scaling laws) and apply them
to the sun, several test cases and three stars.
The SOLA approach and the scaling law based on the surface correcting
technique described by Kjeldsen et al. (2008) yield comparable results which
can reach an accuracy of 0.5 % and are better than scaling the large frequency
separation. The reason for this is that the averaging kernels from the two
first methods are comparable in quality and are better than what is obtained
with the large frequency separation. It is also shown that scaling the large
frequency separation is more sensitive to near-surface effects, but is much
less affected by an incorrect mode identification. As a result, one can
identify pulsation modes by looking for an l and n assignment which provides
the best agreement between the results from the large frequency separation and
those from one of the two other methods. Non-linear effects are also discussed
as is the effects of mixed modes. In particular, it is shown that mixed modes
bring little improvement as a result of their poorly adapted kernels.Comment: Accepted for publication in A&A, 20 pages, 19 figure
Thyroid uptake studies in infectious hepatitis
Thyroid-function studies were done in 43 cases of infectious hepatitis with varying degree of liver damage as judged by serum bilirubin levels. A different pattern of thyroid uptakes was seen in patients with moderate liver damage and those with severe liver damage. A good correlation was observed between thyroid uptake and degree of liver damage
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