14,151 research outputs found
Changes in Dark Matter Properties After Freeze-Out
The properties of the dark matter that determine its thermal relic abundance
can be very different from the dark matter properties today. We investigate
this possibility by coupling a dark matter sector to a scalar that undergoes a
phase transition after the dark matter freezes out. If the value of Omega_DM
h^2 calculated from parameters measured at colliders and by direct and indirect
detection experiments does not match the astrophysically observed value, a
novel cosmology of this type could provide the explanation. This mechanism also
has the potential to account for the "boost factor" required to explain the
PAMELA data.Comment: 5 pages; v2: Fixed minor typo, added short discussion of application
to PAMELA and appropriate references, results unchange
Pluto's Light Curve in 1933-1934
We are reporting on a new accurate photographic light curve of Pluto for
1933-1934 when the heliocentric distance was 40 AU. We used 43 B-band and
V-band images of Pluto on 32 plates taken on 15 nights from 19 March 1933 to 10
March 1934. Most of these plates were taken with the Mount Wilson 60" and 100"
telescopes, but 7 of the plates (now at the Harvard College Observatory) were
taken with the 12" and 16" Metcalf doublets at Oak Ridge. The plates were
measured with an iris diaphragm photometer, which has an average one-sigma
photometric error on these plates of 0.08 mag as measured by the repeatability
of constant comparison stars. The modern B and V magnitudes for the comparison
stars were measured with the Lowell Observatory Hall 1.1-m telescope. The
magnitudes in the plate's photographic system were converted to the Johnson B-
and V-system after correction with color terms, even though they are small in
size. We find that the average B-band mean opposition magnitude of Pluto in
1933-1934 was 15.73 +- 0.01, and we see a roughly sinusoidal modulation on the
rotational period (6.38 days) with a peak-to-peak amplitude of 0.11 +- 0.03
mag. With this, we show that Pluto darkened by 5% from 1933-1934 to 1953-1955.
This darkening from 1933-1934 to 1953-1955 cannot be due to changing viewing
geometry (as both epochs had identical sub-Earth latitudes), so our
observations must record a real albedo change over the southern hemisphere. The
later darkening trend from 1954 to the 1980s has been explained by changing
viewing geometry (as more of the darker northern hemisphere comes into view).
Thus, we now have strong evidence for albedo changes on the surface of Pluto,
and these are most easily explained by the systematic sublimation of frosts
from the sunward pole that led to a drop in the mean surface albedo.Comment: Icarus in press, 24 page
Simulation synergy : expanding TRNSYS capabilities and usability
Developers of simulation packages are now able to take advantage of the increase in available desktop computing power to expand the capabilities and usability of their programs. This paper will illustrate these opportunities by discussing the different techniques the developers of the TRNSYS software package have used to try and create a synergy between TRNSYS and external programs and between the developers and users of the program
On the uniqueness of community banks
To the public, all banks seem alike. But banking insiders make important distinctions between community banks and all other banks. Policymakers worry that community banks’ unique characteristics threaten their survival in the face of industry consolidation. However, despite dramatic regulatory and technological changes in the industry in the past two decades, community banks have not only survived but often prospered. ; This article explores the differences between community banks and larger banks to discover what makes community banks unique. Large banks engage primarily in transactional banking—the provision of highly standardized intermediation services, such as gathering deposits and extending loans, that require little human input to manage. Community banks, in contrast, typically focus on relationship banking, which requires more human input, more detailed credit evaluation, and localized decision making. ; Examining profit and risk measures for the 1998–2002 period for both community banks and large banking organizations, the authors find evidence that small banks were generally profitable. In all but the smallest size category, community banks have performed as well as, and often better than, large banks in managing net interest margins, aggregate profits, and credit risk. Also, community banks are more likely to adopt Subchapter S tax status, which allows them to avoid direct federal income taxation and pass tax benefits on to shareholders. These institutions typically have relatively higher returns on both equity and assets than larger banks do. Whether community banks will be able to sustain this good performance will depend, the authors conclude, on how well managers find valuable relationship lending niches, invest bank capital, and balance asset quality with growth.Community banks
A Limited Habitable Zone for Complex Life
The habitable zone (HZ) is commonly defined as the range of distances from a
host star within which liquid water, a key requirement for life, may exist on a
planet's surface. Substantially more CO2 than present in Earth's modern
atmosphere is required to maintain clement temperatures for most of the HZ,
with several bars required at the outer edge. However, most complex aerobic
life on Earth is limited by CO2 concentrations of just fractions of a bar. At
the same time, most exoplanets in the traditional HZ reside in proximity to M
dwarfs, which are more numerous than Sun-like G dwarfs but are predicted to
promote greater abundances of gases that can be toxic in the atmospheres of
orbiting planets, such as carbon monoxide (CO). Here we show that the HZ for
complex aerobic life is likely limited relative to that for microbial life. We
use a 1D radiative-convective climate and photochemical models to circumscribe
a Habitable Zone for Complex Life (HZCL) based on known toxicity limits for a
range of organisms as a proof of concept. We find that for CO2 tolerances of
0.01, 0.1, and 1 bar, the HZCL is only 21%, 32%, and 50% as wide as the
conventional HZ for a Sun-like star, and that CO concentrations may limit some
complex life throughout the entire HZ of the coolest M dwarfs. These results
cast new light on the likely distribution of complex life in the universe and
have important ramifications for the search for exoplanet biosignatures and
technosignatures.Comment: Revised including additional discussion. Published Gold OA in ApJ. 9
pages, 5 figures, 5 table
Supersymmetric Baryogenesis from Exotic Quark Decays
In a simple extension of the minimal supersymmetric standard model,
out-of-equilibrium decays of TeV scale exotic vector-like squarks may generate
the baryon asymmetry of the universe. Baryon number and CP violation are
present in the superpotential, so this mechanism does not rely on CP violation
in supersymmetry breaking parameters. We discuss phenomenological constraints
on the model as well as potential signals for the Large Hadron Collider and
electronic dipole moment experiments. A variation on the TeV scale model allows
the exotic squarks to be the messengers of gauge mediated supersymmetry
breaking.Comment: 28 pages, 7 figures, 2 appendices, v2: typos corrected, results
unchange
Green Revolution Counterfactuals
In this paper, we conduct two "counterfactual" simulations for the 30-year period 1970-2000-the first holding 1970 crop genetic improvements (CGI) constant and the second presuming the International Agricultural Research Center (IARC) system had not been built. Both these counterfactuals apply to developing countries only. The core estimates on which the counterfactuals are based include country fixed effects , and the key estimates are for the Dietary Energy Sufficiency (DES) equation. DES affects birth rates, death rates, child mortality rates and malnutrition rates, making it possible to "endogenize" population growth in developing countries, in the counterfactuals. Reduced DES levels (from reduced CGI contributions) will lead to more births, more deaths and more child deaths and higher levels of malnutrition. The key technology variables that determine DES are the number of agricultural scientists per million hectares of cropland, the average years of schooling of adult males (over 25), and the level of Green Revolution Modern Varieties (GRMV) adoption. Our results show striking contrasts between the historical record and the alternative counterfactuals. The worst outcome is that without any Green Revolution Technologies or an IARC system to support it, which results in holding technological advancements constant at the 1970 level is a marginal improvement, leading to much higher prices over time, as agricultural production struggles to keep up with food demand in those countries. The endogenous feedback effects of population show the importance of nutrition and education, and argue strongly in favor of those factors playing a significant role in the improvement of human well-being that has been observed since the start of the Green Revolution to present.Research and Development/Tech Change/Emerging Technologies,
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