1,556 research outputs found
Seismology of the Sun : Inference of Thermal, Dynamic and Magnetic Field Structures of the Interior
Recent overwhelming evidences show that the sun strongly influences the
Earth's climate and environment. Moreover existence of life on this Earth
mainly depends upon the sun's energy. Hence, understanding of physics of the
sun, especially the thermal, dynamic and magnetic field structures of its
interior, is very important. Recently, from the ground and space based
observations, it is discovered that sun oscillates near 5 min periodicity in
millions of modes. This discovery heralded a new era in solar physics and a
separate branch called helioseismology or seismology of the sun has started.
Before the advent of helioseismology, sun's thermal structure of the interior
was understood from the evolutionary solution of stellar structure equations
that mimicked the present age, mass and radius of the sun. Whereas solution of
MHD equations yielded internal dynamics and magnetic field structure of the
sun's interior. In this presentation, I review the thermal, dynamic and
magnetic field structures of the sun's interior as inferred by the
helioseismology.Comment: To be published in the proceedings of the meeting "3rd International
Conference on Current Developments in Atomic, Molecular, Optical and Nano
Physics with Applications", December 14-16, 2011, New Delhi, Indi
Fast, exact CMB power spectrum estimation for a certain class of observational strategies
We describe a class of observational strategies for probing the anisotropies
in the cosmic microwave background (CMB) where the instrument scans on rings
which can be combined into an n-torus, the {\em ring torus}. This class has the
remarkable property that it allows exact maximum likelihood power spectrum
estimation in of order operations (if the size of the data set is )
under circumstances which would previously have made this analysis intractable:
correlated receiver noise, arbitrary asymmetric beam shapes and far side lobes,
non-uniform distribution of integration time on the sky and partial sky
coverage. This ease of computation gives us an important theoretical tool for
understanding the impact of instrumental effects on CMB observables and hence
for the design and analysis of the CMB observations of the future. There are
members of this class which closely approximate the MAP and Planck satellite
missions. We present a numerical example where we apply our ring torus methods
to a simulated data set from a CMB mission covering a 20 degree patch on the
sky to compute the maximum likelihood estimate of the power spectrum
with unprecedented efficiency.Comment: RevTeX, 14 pages, 5 figures. A full resolution version of Figure 1
and additional materials are at http://feynman.princeton.edu/~bwandelt/RT
Temperature and Polarization Patterns in Anisotropic Cosmologies
We study the coherent temperature and polarization patterns produced in
homogeneous but anisotropic cosmological models. We show results for all
Bianchi types with a Friedman-Robertson-Walker limit (i.e. Types I, V,
VII, VII and IX) to illustrate the range of possible behaviour. We
discuss the role of spatial curvature, shear and rotation in the geodesic
equations for each model and establish some basic results concerning the
symmetries of the patterns produced. We also give examples of the
time-evolution of these patterns in terms of the Stokes parameters , and
.Comment: 24 pages, 7 Figures, submitted to JCAP. Revised version: numerous
references added, text rewritten, and errors corrected
Halogen atom participation in guiding the stereochemical outcomes of acetal substitution reactions
Bio-organic Synthesi
Single-Proton Removal Reaction Study of 16B
The low-lying level structure of the unbound system B has been
investigated via single-proton removal from a 35 MeV/nucleon C beam. The
coincident detection of the beam velocity B fragment and neutron allowed
the relative energy of the in-flight decay of B to be reconstructed. The
resulting spectrum exhibited a narrow peak some 85 keV above threshold. It is
argued that this feature corresponds to a very narrow (100 keV)
resonance, or an unresolved multiplet, with a dominant + configuration which decays by d-wave neutron
emission.Comment: 16 pages, 5 figures, 1 table, submitted to Phys. Lett.
Photoassociation spectroscopy of cold calcium atoms
Photoassociation spectroscopy experiments on 40Ca atoms close to the
dissociation limit 4s4s 1S0 - 4s4p 1P1 are presented. The vibronic spectrum was
measured for detunings of the photoassociation laser ranging from 0.6 GHz to 68
GHz with respect to the atomic resonance. In contrast to previous measurements
the rotational splitting of the vibrational lines was fully resolved. Full
quantum mechanical numerical simulations of the photoassociation spectrum were
performed which allowed us to put constraints on the possible range of the
calcium scattering length to between 50 a_0 and 300 a_0
Constraints on cosmic hemispherical power anomalies from quasars
Recent analyses of the cosmic microwave background (CMB) maps from the WMAP
satellite have uncovered evidence for a hemispherical power anomaly, i.e. a
dipole modulation of the CMB power spectrum at large angular scales with an
amplitude of +/-14 percent. Erickcek et al have put forward an inflationary
model to explain this anomaly. Their scenario is a variation on the curvaton
scenario in which the curvaton possesses a large-scale spatial gradient that
modulates the amplitude of CMB fluctuations. We show that this scenario would
also lead to a spatial gradient in the amplitude of perturbations sigma_8, and
hence to a dipole asymmetry in any highly biased tracer of the underlying
density field. Using the high-redshift quasars from the Sloan Digital Sky
Survey, we find an upper limit on such a gradient of |nabla
sigma_8|/sigma_8<0.027/r_{lss} (99% posterior probability), where r_{lss} is
the comoving distance to the last-scattering surface. This rules out the
simplest version of the curvaton spatial gradient scenario.Comment: matches JCAP accepted version (minor revisions
Molecular markers for tracking the origin and worldwide distribution of invasive strains of <i>Puccinia striiformis</i>
Investigating the origin and dispersal pathways is instrumental to mitigate threats and economic and environmental consequences of invasive crop pathogens. In the case of Puccinia striiformis causing yellow rust on wheat, a number of economically important invasions have been reported, e.g., the spreading of two aggressive and high temperature adapted strains to three continents since 2000. The combination of sequence-characterized amplified region (SCAR) markers, which were developed from two specific AFLP fragments, differentiated the two invasive strains, PstS1 and PstS2 from all other P. striiformis strains investigated at a worldwide level. The application of the SCAR markers on 566 isolates showed that PstS1 was present in East Africa in the early 1980s and then detected in the Americas in 2000 and in Australia in 2002. PstS2 which evolved from PstS1 became widespread in the Middle East and Central Asia. In 2000, PstS2 was detected in Europe, where it never became prevalent. Additional SSR genotyping and virulence phenotyping revealed 10 and six variants, respectively, within PstS1 and PstS2, demonstrating the evolutionary potential of the pathogen. Overall, the results suggested East Africa as the most plausible origin of the two invasive strains. The SCAR markers developed in the present study provide a rapid, inexpensive, and efficient tool to track the distribution of P. striiformis invasive strains, PstS1 and PstS2
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