3,844 research outputs found
The Effect of Asymmetric Beams in the Wilkinson Microwave Anisotropy Probe Experiment
We generate simulations of the cosmic microwave background (CMB) temperature field as observed by the Wilkinson Microwave Anisotropy Probe (WMAP) satellite, taking into account the detailed shape of the asymmetric beams and scanning strategy of the experiment, and use these to re-estimate the WMAP beam transfer functions. This method avoids the need of artificially symmetrizing the beams, as done in the baseline WMAP approach, and instead measures the total convolution effect by direct simulation. We find only small differences with respect to the nominal transfer functions, typically less than 1% everywhere, and less than 0.5% at ℓ < 400. The net effect on the CMB power spectrum is less than 0.6%. The effect on all considered cosmological parameters is negligible. For instance, we find that the spectral index of scalar perturbations after taking into account the beam asymmetries is n_s = 0.964 ± 0.014, corresponding to a negative shift of –0.1σ compared to the previously released WMAP results. Our CMB sky simulations are made publicly available and can be used for general studies of asymmetric beam effects in the WMAP data
Observing Spontaneous Strong Parity Violation in Heavy-Ion Collisions
We discuss the problem of observing spontaneous parity and CP violation in
collision systems. We discuss and propose observables which may be used in
heavy-ion collisions to observe such violations, as well as event-by-event
methods to analyze the data. Finally, we discuss simple monte-carlo models of
these CP violating effects which we have used to develop our techniques and
from which we derive rough estimates of sensitivities to signals which may be
seen at RHIC
Investigation of the radiative boundary conditions during the development of the southwest monsoon Saudi Arabian heat low, An
January 1982.Includes bibliographical references.Progress report no. 2 on the cooperative research project between the Department of Atmospheric Science at Colorado State University and the Faculty of Meteorology and Environmental Science at King Abdul-Aziz University in accordance with the CID-ARME TED Project of the University of Arizona. Period covered August 16-November 30, 1981.CID contract #CSU-SA-KAU-02
The efficacy of aerosol–cloud radiative perturbations from near-surface emissions in deep open-cell stratocumuli
Aerosol–cloud radiative effects are determined and quantified in simulations
of deep open-cell stratocumuli observed during the VAMOS Ocean-Cloud-Atmosphere-Land
Study Regional Experiment (VOCALS-REx) campaign off
the west coast of Chile. The cloud deck forms in a boundary
layer 1.5 km deep, with cell sizes reaching 50 km in diameter. Global databases of ship
tracks suggest that these linear structures are seldom found in boundary
layers this deep. Here, we quantify the changes in cloud radiative properties
to a continuous aerosol point source moving along a fixed emission line
releasing 1017 particles per second. We show that a spatially coherent
cloud perturbation is not evident along the emission line. Yet our model
simulates an increase in domain-mean all-sky albedo of 0.05, corresponding to
a diurnally averaged cloud radiative effect of 20 W m−2, given the
annual mean solar insolation at the VOCALS-REx site. Therefore, marked
changes in cloud radiative properties in precipitating deep open cells may be
driven by anthropogenic near-surface aerosol perturbations, such as those
generated by ships.
Furthermore, we demonstrate that these changes in cloud radiative properties
are masked by the naturally occurring variability within the organised cloud
field. A clear detection and attribution of cloud radiative effects to a
perturbation in aerosol concentrations becomes possible when sub-filtering of
the cloud field is applied, using the spatio-temporal distribution of the
aerosol perturbation. Therefore, this work has implications for the detection
and attribution of effective cloud radiative forcing in marine stratocumuli,
which constitutes one of the major physical uncertainties within the climate
system. Our results suggest that ships may sometimes have a substantial
radiative effect on marine clouds and albedo, even when ship tracks are not
readily visible.</p
Frequentist comparison of CMB local extrema statistics in the five-year WMAP data with two anisotropic cosmological models
We present local extrema studies of two models that introduce a preferred
direction into the observed cosmic microwave background (CMB) temperature
field. In particular, we make a frequentist comparison of the one- and
two-point statistics for the dipole modulation and ACW models with data from
the five-year Wilkinson Microwave Anisotropy Probe (WMAP). This analysis is
motivated by previously revealed anomalies in the WMAP data, and particularly
the difference in the statistical nature of the temperature anisotropies when
analysed in hemispherical partitions.
The analysis of the one-point statistics indicates that the previously
determined hemispherical variance difficulties can be apparently overcome by a
dipole modulation field, but new inconsistencies arise if the mean and the
l-dependence of the statistics are considered. The two-point correlation
functions of the local extrema, the temperature pair product and the
point-point spatial pair-count, demonstrate that the impact of such a
modulation is to over-`asymmetrise' the temperature field on smaller scales
than the wave-length of the dipole or quadrupole, and this is disfavored by the
observed data.The results from the ACW model predictions, however, are
consistent with the standard isotropic hypothesis. The two-point analysis
confirms that the impact of this type of violation of isotropy on the
temperature extrema statistics is relatively weak.
From this work, we conclude that a model with more spatial structure than the
dipole modulated or rotational-invariance breaking models are required to fully
explain the observed large-scale anomalies in the WMAP data.Comment: 10 pages, 4 figures, 3 tables, accepted for publication in MNRA
The mechanism of twin thickening and the elastic strain state of TWIP steel nanotwins
A Twinning Induced Plasticity (TWIP) steel with a nominal composition of
Fe-16.4Mn-0.9C-0.5Si-0.05Nb-0.05V was deformed to an engineering strain of 6\%.
The strain around the deformation twins were mapped using the 4D-STEM
technique. Strain mapping showed a large average elastic strain of
approximately 6\% in the directions parallel and perpendicular to the twinning
direction. However, the large average strain comprised of several hot spots of
even larger strains of up to 12\%. These hot spots could be attributed to a
high density of sessile Frank dislocations on the twin boundary and correspond
to shear stresses of 1--1.5 GPa. The strain and therefore stress fields are
significantly larger than other materials known to twin and are speculated to
be responsible for the early thickness saturation of TWIP steel nanotwins. The
ability to keep twins extremely thin helps improve grain fragmentation,
\textit{i.e.} the dynamic Hall-Petch effect, and underpins the large
elongations and strain hardening rates in TWIP steels
Resolution of severe pyoderma gangrenosum in a patient with streaking leukocyte factor disease after treatment with tacrolimus (FK 506)
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