2,190 research outputs found
Live and Feeder Cattle Options Markets: Returns, Risk, and Volatility Forecasting
The paper examines empirical returns from holding thirty- and ninety-day call and put positions, and the forecasting performance of implied volatility in the live and feeder cattle options markets. In both markets, implied volatility is an upwardly biased and inefficient predictor of realized volatility, with bias most prominent in live cattle. While significant returns exist holding several market positions, most strategies are strongly affected by a drift in futures market prices. However, the returns from selling live cattle puts are persistent, and evidence from straddle returns identifies that the market overprices volatility. This overpricing is consistent with a short-term risk premium whose effect is magnified by extreme changes in market conditions.live cattle, feeder cattle, options, returns, risk, volatility forecasting, Agribusiness, Agricultural and Food Policy, Agricultural Finance, Community/Rural/Urban Development, Farm Management, Financial Economics, Livestock Production/Industries, Marketing, Research Methods/ Statistical Methods,
Discovery of High-Latitude CO in a HI Supershell in NGC 5775
We report the discovery of very high latitude molecular gas in the edge-on
spiral galaxy, NGC 5775. Emission from both the J=1-0 and 2-1 lines of 12CO is
detected up to 4.8 kpc away from the mid-plane of the galaxy. NGC 5775 is known
to host a number of HI supershells. The association of the molecular gas
M(H2,F2) = 3.1x10^7 solar masses reported here with one of the HI supershells
(labeled F2) is clear, which suggests that molecular gas may have survived the
process which originally formed the supershell. Alternatively, part of the gas
could have been formed in situ at high latitude from shock-compression of
pre-existing HI gas. The CO J=2-1/J=1-0 line ratio of 0.34+-40% is
significantly lower than unity, which suggests that the gas is excited
subthermally, with gas density a few times 100 cubic cm. The molecular gas is
likely in the form of cloudlets which are confined by magnetic and cosmic rays
pressure. The potential energy of the gas at high latitude is found to be
2x10^56 ergs and the total (HI + H2) kinetic energy is 9x10^53 ergs. Based on
the energetics of the supershell, we suggest that most of the energy in the
supershell is in the form of potential energy and that the supershell is on the
verge of falling and returning the gas to the disk of the galaxy.Comment: Accept by ApJL, 4 pages, 3 ps figure
SERVIR: From Space to Village. A Regional Monitoring and Visualization System For Environmental Management Using Satellite Applications For Sustainable Development
NASA is committed to providing technological support and expertise to regional and national organizations for earth science monitoring and analysis. This commitment is exemplified by NASA's long-term relationship with Central America. The focus of these efforts has primarily been to measure the impact of human development on the environment and to provide data for the management of human settlement and expansion in the region. Now, NASA is planning to extend and expand this capability to other regions of the world including Africa and the Caribbean. NASA began using satellite imagery over twenty-five years ago to locate important Maya archeological sites in Mesoamerica and to quantify the affect of deforestation on those sites. Continuing that mission, NASA has partnered with the U.S. Agency for International Development (USAID), the World Bank, the Water Center for the Humid Tropics of Latin America and the Caribbean (CATHALAC) and the Central American Commission for Environment and Development (CCAD) to develop SERVIR (Sistema Regional de Visualizacion y Monitoreo), for the Mesoamerican Biological Corridor. SERVIR has become one of the most important aspects of NASA's geospatial efforts in Central America by establishing a common access portal for information that affects the lives, livelihood and future of everyone in the region. SERVIR, most commonly referred to as a regional visualization and monitoring system, is a scientific and technological platform that integrates satellite and other geospatial data sets to generate tools for improved decision-making capabilities. It has a collection of data and models that are easily accessible to earth science managers, first responders, NGO's (Non-Government Organizations) and a host of others. SERVIR is currently used to monitor and forecast ecological changes as well as provide information for decision support during severe events such as forest fires, red tides,and tropical storms. Additionally, SERVIR addresses the nine societal benefit areas of the Global Earth Observation System (GEOSS): disasters, ecosystems, biodiversity, weather, water, climate, health, agriculture and energy
Understanding and Mitigating Biases when Studying Inhomogeneous Emission Spectra with JWST
Exoplanet emission spectra are often modelled assuming that the hemisphere
observed is well represented by a horizontally homogenised atmosphere. However
this approximation will likely fail for planets with a large temperature
contrast in the James Webb Space Telescope (JWST) era, potentially leading to
erroneous interpretations of spectra. We first develop an analytic formulation
to quantify the signal-to-noise ratio and wavelength coverage necessary to
disentangle temperature inhomogeneities from a hemispherically averaged
spectrum. We find that for a given signal-to-noise ratio, observations at
shorter wavelengths are better at detecting the presence of inhomogeneities. We
then determine why the presence of an inhomogeneous thermal structure can lead
to spurious molecular detections when assuming a fully homogenised planet in
the retrieval process. Finally, we quantify more precisely the potential biases
by modelling a suite of hot Jupiter spectra, varying the spatial contributions
of a hot and a cold region, as would be observed by the different instruments
of JWST/NIRSpec. We then retrieve the abundances and temperature profiles from
the synthetic observations. We find that in most cases, assuming a homogeneous
thermal structure when retrieving the atmospheric chemistry leads to biased
results, and spurious molecular detection. Explicitly modelling the data using
two profiles avoids these biases, and is statistically supported provided the
wavelength coverage is wide enough, and crucially also spanning shorter
wavelengths. For the high contrast used here, a single profile with a dilution
factor performs as well as the two-profile case, with only one additional
parameter compared to the 1-D approach.Comment: Accepted for publication by MNRA
How Does Thermal Scattering Shape the Infrared Spectra of Cloudy Exoplanets? A Theoretical Framework and Consequences for Atmospheric Retrievals in the JWST era
Observational studies of exoplanets are suggestive of a ubiquitous presence
of clouds. The current modelling techniques used in emission to account for the
clouds tend to require prior knowledge of the cloud condensing species and
often do not consider the scattering effects of the cloud. We explore the
effects that thermal scattering has on the emission spectra by modelling a
suite of hot Jupiter atmospheres with varying cloud single-scattering albedos
(SSAs) and temperature profiles. We examine cases ranging from simple
isothermal conditions to more complex structures and physically driven cloud
modelling. We show that scattering from nightside clouds would lead to
brightness temperatures that are cooler than the real atmospheric temperature
if scattering is unaccounted for. We show that scattering can produce spectral
signatures in the emission spectrum even for isothermal atmospheres. We
identify the retrieval degeneracies and biases that arise in the context of
simulated JWST spectra when the scattering from the clouds dominates the
spectral shape. Finally, we propose a novel method of fitting the SSA spectrum
of the cloud in emission retrievals, using a technique that does not require
any prior knowledge of the cloud chemical or physical properties.Comment: Accepted to MNRA
The effect of using different reference dates for control exposure measurement on relative risk estimates in a case-control study
Artículo científico -- Universidad de Costa Rica, Instituto de Investigaciones en Saud. 1993. Debido a las políticas de la revista en la que el artículo fue publicado, no es posible distribuir la edición del editor/PDF.In case-control studies in which case and control enrollment periods are not identical, exposure status for time-dependent variables is often measured relative to a reference date. Using data from a case-control study of the relation between cervical cancer and oral contraceptive (OC) use in which control enrollment began 6 months after the end of case enrollment, we evaluated the effect on odds ratios from using five different reference dates to determine the controls' exposure status. The choice of reference date had little effect on the odds ratios in this study. Reference dates for time-dependent exposure variables should be considered carefully in studies when case and control enrollment periods are not identical.Universidad de Costa Rica, Instituto de Investigaciones en SaludUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias de la Salud::Instituto de Investigaciones en Salud (INISA
PAHs in the Halo of NGC 5529
We present sensitive ISO m observations of the edge-on
galaxy, NGC 5529, finding an extensive MIR halo around NGC 5529. The emission
is dominated by PAHs in this band. The PAH halo has an exponential scale height
of 3.7 kpc but can still be detected as far as kpc from the plane
to the limits of the high dynamic range (1770/1) data. This is the most
extensive PAH halo yet detected in a normal galaxy. This halo shows
substructure and the PAHs likely originate from some type of disk outflow. PAHs
are long-lived in a halo environment and therefore continuous replenishment
from the disk is not required (unless halo PAHs are also being destroyed or
removed), consistent with the current low SFR of the galaxy. The PAHs correlate
spatially with halo H emission, previously observed by Miller &
Veilleux (2003); both components are likely excited/ionized by in-disk photons
that are leaking into the halo. The presence of halo gas may be related to the
environment of NGC 5529 which contains at least 17 galaxies in a small group of
which NGC 5529 is the dominant member. Of these, we have identified two new
companions from the SDSS.Comment: 16 pages, 5 gif figures, accepted for publication in A&A, For pdf
with higher quality figures, see http://www.astro.queensu.ca/~irwi
K Corrections For Type Ia Supernovae and a Test for Spatial Variation of the Hubble Constant
Cross-filter K corrections for a sample of "normal" Type Ia supernovae (SNe)
have been calculated for a range of epochs. With appropriate filter choices,
the combined statistical and systematic K correction dispersion of the full
sample lies within 0.05 mag for redshifts z<0.7. This narrow dispersion of the
calculated K correction allows the Type Ia to be used as a cosmological probe.
We use the K corrections with observations of seven SNe at redshifts 0.3 < z
<0.5 to bound the possible difference between the locally measured Hubble
constant (H_L) and the true cosmological Hubble constant (H_0).Comment: 6 pages, 3 Postscript figures, uuencoded uses crckapb.sty and
psfig.sty. To appear in Thermonuclear Supernovae (NATO ASI), eds. R. Canal,
P. Ruiz-LaPuente, and J. Isern. Postscript version is also available at
http://www-supernova.lbl.gov
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AKAP12 Mediates Barrier Functions of Fibrotic Scars during CNS Repair
The repair process after CNS injury shows a well-organized cascade of three distinct stages: inflammation, new tissue formation, and remodeling. In the new tissue formation stage, various cells migrate and form the fibrotic scar surrounding the lesion site. The fibrotic scar is known as an obstacle for axonal regeneration in the remodeling stage. However, the role of the fibrotic scar in the new tissue formation stage remains largely unknown. We found that the number of A-kinase anchoring protein 12 (AKAP12)-positive cells in the fibrotic scar was increased over time, and the cells formed a structure which traps various immune cells. Furthermore, the AKAP12-positive cells strongly express junction proteins which enable the structure to function as a physical barrier. In in vivo validation, AKAP12 knock-out (KO) mice showed leakage from a lesion, resulting from an impaired structure with the loss of the junction complex. Consistently, focal brain injury in the AKAP12 KO mice led to extended inflammation and more severe tissue damage compared to the wild type (WT) mice. Accordingly, our results suggest that AKAP12-positive cells in the fibrotic scar may restrict excessive inflammation, demonstrating certain mechanisms that could underlie the beneficial actions of the fibrotic scar in the new tissue formation stage during the CNS repair process
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