250,547 research outputs found
Consistency of cosmic microwave background temperature measurements in three frequency bands in the 2500-square-degree SPT-SZ survey
We present an internal consistency test of South Pole Telescope (SPT)
measurements of the cosmic microwave background (CMB) temperature anisotropy
using three-band data from the SPT-SZ survey. These measurements are made from
observations of ~2500 deg^2 of sky in three frequency bands centered at 95,
150, and 220 GHz. We combine the information from these three bands into six
semi-independent estimates of the CMB power spectrum (three single-frequency
power spectra and three cross-frequency spectra) over the multipole range 650 <
l < 3000. We subtract an estimate of foreground power from each power spectrum
and evaluate the consistency among the resulting CMB-only spectra. We determine
that the six foreground-cleaned power spectra are consistent with the null
hypothesis, in which the six cleaned spectra contain only CMB power and noise.
A fit of the data to this model results in a chi-squared value of 236.3 for 235
degrees of freedom, and the probability to exceed this chi-squared value is
46%.Comment: 21 pages, 4 figures, current version matches version published in
JCA
Consistency tests in cosmology using relative entropy
With the high-precision data from current and upcoming experiments, it
becomes increasingly important to perform consistency tests of the standard
cosmological model. In this work, we focus on consistency measures between
different data sets and methods that allow us to assess the goodness of fit of
different models. We address both of these questions using the relative entropy
or Kullback-Leibler (KL) divergence [Kullback et al., 1951]. First, we revisit
the relative entropy as a consistency measure between data sets and further
investigate some of its key properties, such as asymmetry and path dependence.
We then introduce a novel model rejection framework, which is based on the
relative entropy and the posterior predictive distribution. We validate the
method on several toy models and apply it to Type Ia supernovae data from the
JLA and CMB constraints from Planck 2015, testing the consistency of the data
with six different cosmological models.Comment: 31 pages, 10 figures, 4 tables, updated following referee's comments,
matches version accepted by JCA
Exploring the Free Energy Landscape: From Dynamics to Networks and Back
The knowledge of the Free Energy Landscape topology is the essential key to
understand many biochemical processes. The determination of the conformers of a
protein and their basins of attraction takes a central role for studying
molecular isomerization reactions. In this work, we present a novel framework
to unveil the features of a Free Energy Landscape answering questions such as
how many meta-stable conformers are, how the hierarchical relationship among
them is, or what the structure and kinetics of the transition paths are.
Exploring the landscape by molecular dynamics simulations, the microscopic data
of the trajectory are encoded into a Conformational Markov Network. The
structure of this graph reveals the regions of the conformational space
corresponding to the basins of attraction. In addition, handling the
Conformational Markov Network, relevant kinetic magnitudes as dwell times or
rate constants, and the hierarchical relationship among basins, complete the
global picture of the landscape. We show the power of the analysis studying a
toy model of a funnel-like potential and computing efficiently the conformers
of a short peptide, the dialanine, paving the way to a systematic study of the
Free Energy Landscape in large peptides.Comment: PLoS Computational Biology (in press
The effects of localized damping on structural response
The effect of localized structural damping on the excitability of higher order normal modes of the large space telescope was investigated. A preprocessor computer program was developed to incorporate Voigt structural joint damping models in a NASTRAN finite-element dynamic model. A postprocessor computer program was developed to select critical modes for low-frequency attitude control problems and for higher frequency fine-stabilization problems. The mode selection is accomplished by ranking the flexible modes based on coefficients for rate gyro, position gyro, and optical sensors, and on image-plane motions due to sinusoidal or random power spectral density force and torque inputs
How Well Do We Know the Orbits of the Outer Planets?
This paper deals with the problem of astrometric determination of the orbital
elements of the outer planets, in particular by assessing the ability of
astrometric observations to detect perturbations of the sort expected from the
Pioneer effect or other small perturbations to gravity. We also show that while
using simplified models of the dynamics can lead to some insights, one must be
careful to not over-simplify the issues involved lest one be misled by the
analysis onto false paths. Specifically, we show that the current ephemeris of
Pluto does not preclude the existence of the Pioneer effect. We show that the
orbit of Pluto is simply not well enough characterized at present to make such
an assertion. A number of misunderstandings related to these topics have now
propagated through the literature and have been used as a basis for drawing
conclusions about the dynamics of the solar system. Thus, the objective of this
paper is to address these issues. Finally, we offer some comments dealing with
the complex topic of model selection and comparison.Comment: Accepted for publication in the Ap
Density dependence of the s-wave repulsion in pionic atoms
Several mechanisms of density dependence of the s-wave repulsion in pionic
atoms, beyond the conventional model, are tested by parameter fits to a large
(106 points) set of data from O to U, including `deeply bound'
states in Pb. Special attention is paid to the proper choice of nuclear
density distributions. A density-dependent isovector scattering amplitude
suggested recently by Weise to result from a density dependence of the pion
decay constant is introduced and found to account for most of the so-called
anomalous repulsion. The presence of such an effect might indicate partial
chiral symmetry restoration in dense matter. The anomalous repulsion is fully
accounted for when an additional relativistic impulse approximation term is
included in the potential.Comment: 18 pages, 5 figures, version 2 (extended
Sachs' free data in real connection variables
We discuss the Hamiltonian dynamics of general relativity with real
connection variables on a null foliation, and use the Newman-Penrose formalism
to shed light on the geometric meaning of the various constraints. We identify
the equivalent of Sachs' constraint-free initial data as projections of
connection components related to null rotations, i.e. the translational part of
the ISO(2) group stabilising the internal null direction soldered to the
hypersurface. A pair of second-class constraints reduces these connection
components to the shear of a null geodesic congruence, thus establishing
equivalence with the second-order formalism, which we show in details at the
level of symplectic potentials. A special feature of the first-order
formulation is that Sachs' propagating equations for the shear, away from the
initial hypersurface, are turned into tertiary constraints; their role is to
preserve the relation between connection and shear under retarded time
evolution. The conversion of wave-like propagating equations into constraints
is possible thanks to an algebraic Bianchi identity; the same one that allows
one to describe the radiative data at future null infinity in terms of a shear
of a (non-geodesic) asymptotic null vector field in the physical spacetime.
Finally, we compute the modification to the spin coefficients and the null
congruence in the presence of torsion.Comment: 23 pages + Appendix, 2 figures. v2: Improved text and some amendments
throughout, added more details on the relation between 2+2 foliations and
null tetrads, updated references. Version submitted for peer reviewing. v3:
Few minor amendments, footnote added on a null congruence in the presence of
torsion; matches published versio
Rayleigh-Brillouin light scattering spectroscopy of nitrous oxide (NO)
High signal-to-noise and high-resolution light scattering spectra are
measured for nitrous oxide (NO) gas at an incident wavelength of 403.00 nm,
at 90 scattering, at room temperature and at gas pressures in the range
bar. The resulting Rayleigh-Brillouin light scattering spectra are
compared to a number of models describing in an approximate manner the
collisional dynamics and energy transfer in this gaseous medium of this
polyatomic molecular species. The Tenti-S6 model, based on macroscopic gas
transport coefficients, reproduces the scattering profiles in the entire
pressure range at less than 2\% deviation at a similar level as does the
alternative kinetic Grad's 6-moment model, which is based on the internal
collisional relaxation as a decisive parameter. A hydrodynamic model fails to
reproduce experimental spectra for the low pressures of 0.5-1 bar, but yields
very good agreement (\%) in the pressure range bar. While these
three models have a different physical basis the internal molecular relaxation
derived can for all three be described in terms of a bulk viscosity of Pas. A 'rough-sphere' model, previously
shown to be effective to describe light scattering in SF gas, is not found
to be suitable, likely in view of the non-sphericity and asymmetry of the N-N-O
structured linear polyatomic molecule
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