1,945 research outputs found
Comparative genetic resistance to Ascaridia galli infections of 4 different commercial layer-lines
1. The objective of the study was to compare the establishment and effect of Ascaridia galli infections in 4 different layer-lines.
2. A total of 160 birds comprising 4 different commercial layer-lines, ISA Brown, New Hampshire, Skalborg and a cross of New Hampshire(NH) and Skalborg (Sk), were infected with A. galli eggs. The birds were examined for the presence of parasite eggs and parasites at weeks 3, 6 and 9 post infection (pi).
3. At week 6 pi the chickens of the NH line harboured more larvae compared with the three other lines. The Sk line chickens excreted more A. galli eggs throughout the study compared with the other lines. Female worms in the Sk line were more fecund than the worms in the other lines. Male and female worms recovered from the Sk line at week 9 pi were longer. Male worms recovered from the NH line 6 weeks pi were shorter than male worms from the other lines. Female worms recovered from the NH line were shorter than the female worms from the ISA line and the Sk line. No differences were seen
in weight gain among the 4 lines.
4. The results suggest that genetic factors are involved in the establishment and survival of A. galli in the intestine of layers. Further studies are needed to elucidate the genetic mechanisms behind the observed parasitological findings
Three-dimensional stability of the solar tachocline
The three-dimensional, hydrodynamic stability of the solar tachocline is
investigated based on a rotation profile as a function of both latitude and
radius. By varying the amplitude of the latitudinal differential rotation, we
find linear stability limits at various Reynolds numbers by numerical
computations. We repeated the computations with different latitudinal and
radial dependences of the angular velocity. The stability limits are all higher
than those previously found from two-dimensional approximations and higher than
the shear expected in the Sun. It is concluded that any part of the tachocline
which is radiative is hydrodynamically stable against small perturbations.Comment: 6 pages, 8 figures, accepted by Astron. & Astrophy
How much more can sunspots tell us about the solar dynamo?
Sunspot observations inspired solar dynamo theory and continue to do so. Simply counting them established the sunspot cycle and its period. Latitudinal distributions introduced the tough constraint that the source of sunspots moves equator-ward as the cycle progresses. Observations of Hale's polarity law mandated hemispheric asymmetry. How much more can sunspots tell us about the solar dynamo? We draw attention to a few outstanding questions raised by inherent sunspot properties. Namely, how to explain sunspot rotation rates, the incoherence of follower spots, the longitudinal spacing of sunspot groups, and brightness trends within a given sunspot cycle. After reviewing the first several topics, we then present new results on the brightness of sunspots in Cycle 24 as observed with the Helioseismic Magnetic Imager (HMI). We compare these results to the sunspot brightness observed in Cycle 23 with the Michelson Doppler Imager (MDI). Next, we compare the minimum intensities of five sunspots simultaneously observed by the Hinode Solar Optical Telescope Spectropolarimeter (SOT-SP) and HMI to verify that the minimum brightness of sunspot umbrae correlates well to the maximum field strength. We then examine 90 and 52 sunspots in the north and south hemisphere, respectively, from 2010 - 2012. Finally, we conclude that the average maximum field strengths of umbra 40 Carrington Rotations into Cycle 24 are 2690 Gauss, virtually indistinguishable from the 2660 Gauss value observed at a similar time in Cycle 23 with MDI
A method for the estimation of p-mode parameters from averaged solar oscillation power spectra
A new fitting methodology is presented which is equally well suited for the
estimation of low-, medium-, and high-degree mode parameters from -averaged
solar oscillation power spectra of widely differing spectral resolution. This
method, which we call the "Windowed, MuLTiple-Peak, averaged spectrum", or
WMLTP Method, constructs a theoretical profile by convolving the weighted sum
of the profiles of the modes appearing in the fitting box with the power
spectrum of the window function of the observing run using weights from a
leakage matrix that takes into account both observational and physical effects,
such as the distortion of modes by solar latitudinal differential rotation. We
demonstrate that the WMLTP Method makes substantial improvements in the
inferences of the properties of the solar oscillations in comparison with a
previous method that employed a single profile to represent each spectral peak.
We also present an inversion for the internal solar structure which is based
upon 6,366 modes that we have computed using the WMLTP method on the 66-day
long 2010 SOHO/MDI Dynamics Run. To improve both the numerical stability and
reliability of the inversion we developed a new procedure for the
identification and correction of outliers in a frequency data set. We present
evidence for a pronounced departure of the sound speed in the outer half of the
solar convection zone and in the subsurface shear layer from the radial sound
speed profile contained in Model~S of Christensen-Dalsgaard and his
collaborators that existed in the rising phase of Solar Cycle~24 during
mid-2010
On the solar origin of the signal at 220.7microHz: A possible component of a g mode?
Gravity modes in the Sun have been the object of a long and difficult search
in recent decades. Thanks to the data accumulated with the last generation of
instruments (BiSON, GONG and three helioseismic instruments aboard SoHO),
scientists have been able to find signatures of their presence. However, the
individual detection of such modes remains evasive. In this article, we study
the signal at 220.7 microHz which is a peak that is present in most of the
helioseismic data of the last 10 years. This signal has already been identified
as being one component of a g-mode candidate detected in the GOLF Doppler
velocity signal. The nature of this peak is studied in particular using the
VIRGO/SPM instrument aboard SoHO. First we analyse all the available
instrumental data of VIRGO and SoHO (housekeeping) to reject any possible
instrumental origin. No relation was found, implying that the signal has a
solar origin. Using Monte Carlo simulations, we find, with more than 99%
confidence level, that the signal found in VIRGO/SPM is very unlikely to be due
to pure noise.Comment: Accepted for publication in ApJSS. 19 pages, 9 figure
The Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Pipeline: Optimization of the Spectral Line Inversion Code
The Very Fast Inversion of the Stokes Vector (VFISV) is a Milne-Eddington
spectral line inversion code used to determine the magnetic and thermodynamic
parameters of the solar photosphere from observations of the Stokes vector in
the 6173 A Fe I line by the Helioseismic and Magnetic Imager (HMI) onboard the
Solar Dynamics Observatory (SDO). We report on the modifications made to the
original VFISV inversion code in order to optimize its operation within the HMI
data pipeline and provide the smoothest solution in active regions. The changes
either sped up the computation or reduced the frequency with which the
algorithm failed to converge to a satisfactory solution. Additionally, coding
bugs which were detected and fixed in the original VFISV release, are reported
here.Comment: Accepted for publication in Solar Physic
Is the solar convection zone in strict thermal wind balance?
Context: The solar rotation profile is conical rather than cylindrical as one
could expect from classical rotating fluid dynamics (e.g. Taylor-Proudman
theorem). Thermal coupling to the tachocline, baroclinic effects and
latitudinal transport of heat have been advocated to explain this peculiar
state of rotation. Aims: To test the validity of thermal wind balance in the
solar convection zone using helioseismic inversions for both the angular
velocity and fluctuations in entropy and temperature. Methods: Entropy and
temperature fluctuations obtained from 3-D hydrodynamical numerical simulations
of the solar convection zone are compared with solar profiles obtained from
helioseismic inversions. Results: The temperature and entropy fluctuations in
3-D numerical simulations have smaller amplitude in the bulk of the solar
convection zone than those found from seismic inversions. Seismic inversion
find variations of temperature from about 1 K at the surface up to 100 K at the
base of the convection zone while in 3-D simulations they are of order 10 K
throughout the convection zone up to 0.96 . In 3-D simulations,
baroclinic effects are found to be important to tilt the isocontours of
away from a cylindrical profile in most of the convection zone helped
by Reynolds and viscous stresses at some locations. By contrast the baroclinic
effect inverted by helioseismology are much larger than what is required to
yield the observed angular velocity profile. Conclusion: The solar convection
does not appear to be in strict thermal wind balance, Reynolds stresses must
play a dominant role in setting not only the equatorial acceleration but also
the observed conical angular velocity profile.Comment: 8 pages, 6 figures (low resolution), Accepted by Astronomy and
Astrophysics - Affiliation: (1) AIM, CEA/DSM-CNRS-Univ. Paris Diderot,
IRFU/SAp, France & (2) LUTH, Observatoire de Paris, CNRS-Univ. Paris Diderot,
France ; (3) Tata Institute of Fundamental Research, India; (4) Centre for
Basic Sciences, University of Mumbai, Indi
Does the Sun Shrink with Increasing Magnetic Activity?
We have analyzed the full set of SOHO/MDI f- and p-mode oscillation
frequencies from 1996 to date in a search for evidence of solar radius
evolution during the rising phase of the current activity cycle. Like Antia et
al. (2000), we find that a significant fraction of the f-mode frequency changes
scale with frequency; and that if these are interpreted in terms of a radius
change, it implies a shrinking sun. Our inferred rate of shrinkage is about 1.5
km/y, which is somewhat smaller than found by Antia et al. We argue that this
rate does not refer to the surface, but rather to a layer extending roughly
from 4 to 8 Mm beneath the visible surface. The rate of shrinking may be
accounted for by an increasing radial component of the rms random magnetic
field at a rate that depends on its radial distribution. If it were uniform,
the required field would be ~7 kG. However, if it were inwardly increasing,
then a 1 kG field at 8 Mm would suffice.
To assess contribution to the solar radius change arising above 4Mm, we
analyzed the p-mode data. The evolution of the p-mode frequencies may be
explained by a magnetic^M field growing with activity. The implications of the
near-surface magnetic field changes depend on the anisotropy of the random
magnetic field. If the field change is predominantly radial, then we infer an
additional shrinking at a rate between 1.1-1.3 km/y at the photosphere. If on
the other hand the increase is isotropic, we find a competing expansion at a
rate of 2.3 km/y. In any case, variations in the sun's radius in the activity
cycle are at the level of 10^{-5} or less, hence have a negligible contribution
to the irradiance variations.Comment: 10 pages (ApJ preprint style), 4 figures; accepted for publication in
Ap
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