3,470 research outputs found
The Standard Cosmological Model and CMB Anisotropies
This is a course on cosmic microwave background (CMB) anisotropies in the
standard cosmological model, designed for beginning graduate students and
advanced undergraduates. ``Standard cosmological model'' in this context means
a Universe dominated by some form of cold dark matter (CDM) with adiabatic
perturbations generated at some initial epoch, e.g., Inflation, and left to
evolve under gravity alone (which distinguishes it from defect models). The
course is primarily theoretical and concerned with the physics of CMB
anisotropies in this context and their relation to structure formation. Brief
presentations of the uniform Big Bang model and of the observed large--scale
structure of the Universe are given. The bulk of the course then focuses on the
evolution of small perturbations to the uniform model and on the generation of
temperature anisotropies in the CMB. The theoretical development is performed
in the (pseudo--)Newtonian gauge because it aids intuitive understanding by
providing a quick reference to classical (Newtonian) concepts. The fundamental
goal of the course is not to arrive at a highly exact nor exhaustive
calculation of the anisotropies, but rather to a good understanding of the
basic physics that goes into such calculations.Comment: Course given at the International School of Space Science: 3K
Cosmology, held in L'Aquila, Italy, September 1998. 44 pages with 4 figure
Further support for the role of heroism in human mate choice
This is an accepted manuscript of an article published by the American Psychological Association in Evolutionary Behavioral Sciences on 03-09-2020.
The accepted version of the publication may differ from the final published version, accessible at https://psycnet.apa.org/doi/10.1037/ebs0000230.Although evidence suggests that altruistic behavior can act as a mating signal, little research has explored the role of heroism in mate choice. Previous research has focused on women only, ignoring the role of heroism in male mate choice. Here, we extended and replicated previous research on the role of heroism in human mate choice. Participants (N=276) rated how desirable targets were for a short-term and long-term relationship, which varied in heroism. The findings showed men and women reported higher desirability for heroic targets for long-term compared to short-term relationships, although this pattern was more prominent in women. These findings add support to the role of heroism in mate choice by exploring the role of heroism in male and female mate choice
Measuring cluster masses with CMB lensing: a statistical approach
We present a method for measuring the masses of galaxy clusters using the
imprint of their gravitational lensing signal on the cosmic microwave
background (CMB) temperature anisotropies. The method first reconstructs the
projected gravitational potential with a quadratic estimator and then applies a
matched filter to extract cluster mass. The approach is well-suited for
statistical analyses that bin clusters according to other mass proxies. We find
that current experiments, such as Planck, the South Pole Telescope and the
Atacama Cosmology Telescope, can practically implement such a statistical
methodology, and that future experiments will reach sensitivities sufficient
for individual measurements of massive systems. As illustration, we use
simulations of Planck observations to demonstrate that it is possible to
constrain the mass scale of a set of 62 massive clusters with prior information
from X-ray observations, similar to the published Planck ESZ-XMM sample. We
examine the effect of the thermal (tSZ) and kinetic (kSZ) Sunyaev-Zeldovich
(SZ) signals, finding that the impact of the kSZ remains small in this context.
The stronger tSZ signal, however, must be actively removed from the CMB maps by
component separation techniques prior to reconstruction of the gravitational
potential. Our study of two such methods highlights the importance of broad
frequency coverage for this purpose. A companion paper presents application to
the Planck data on the ESZ-XMM sample.Comment: 9 pages, 5 figures, version accepted for publication in A&
Point Source Confusion in SZ Cluster Surveys
We examine the effect of point source confusion on cluster detection in
Sunyaev-Zel'dovich (SZ) surveys. A filter matched to the spatial and spectral
characteristics of the SZ signal optimally extracts clusters from the
astrophysical backgrounds. We calculate the expected confusion (point source
and primary cosmic microwave background [CMB]) noise through this filter and
quantify its effect on the detection threshold for both single and multiple
frequency surveys. Extrapolating current radio counts, we estimate that
confusion from sources below 100 microJy limits single-frequency surveys to
1-sigma detection thresholds of Y 3.10^{-6} arcmin^2 at 30 GHz and Y 10^{-5}
arcmin^2 at 15 GHz (for unresolved clusters in a 2 arcmin beam); these numbers
are highly uncertain, and an extrapolation with flatter counts leads to much
lower confusion limits. Bolometer surveys must contend with an important
population of infrared point sources. We find that a three-band matched filter
with 1 arcminute resolution (in each band) efficiently reduces confusion, but
does not eliminate it: residual point source and CMB fluctuations contribute
significantly the total filter noise. In this light, we find that a 3-band
filter with a low-frequency channel (e.g, 90+150+220 GHz) extracts clusters
more effectively than one with a high frequency channel (e.g, 150+220+300 GHz).Comment: Accepted for publication in Astronomy & Astrophysics; Updated grant
information in acknowledgement
Evaluation of installed performance of a wing-tip-mounted pusher turboprop on a semispan wing
An exploratory investigation has been conducted at the Langley Research Center to determine the effect of a wing-tip-mounted pusher turboprop on the aerodynamic characteristics of a semispan wing. Tests were conducted on a semispan model with an upswept, untapered wing and an airdriven motor that powered an SR-2 high-speed propeller located on the tip of the wing as a pusher propeller. All tests were conducted at a Mach number of 0.70 over an angle-of-attack range from approximately -2 to 4 deg at a Reynolds number of 3.82 x 10 to the 6th based on the wing reference chord of 13 in. The data indicate that, as a result of locating the propeller behind the wing trailing edge at the wing tip in the crossflow of the wing-tip vortex, it is possible to improve propeller performance and simultaneously reduce the lift-induced drag
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