257 research outputs found
Feeding behaviour of sheep fed lucerne v. grass hays with controlled post-ingestive consequences
Effect of Condensed Tannins in Sainfoin on \u3cem\u3ein Vitro\u3c/em\u3e Protein Solubility of Lucerne
Proteins of fresh legume forages such as lucerne are highly degraded in the rumen, resulting in their inefficient use by the animal. The condensed tannins (CT) present in some forages can improve the nutritional value of these forages and of associated feeds in the diet. Previous in vitro work (Waghorn & Shelton, 1997) showed that CT from Lotus corniculatus are able to bind with and precipitate protein from a ryegrass/clover pasture, but when these forages were fed to sheep, the CT effects on digestion and animal performance were weak. This revealed a need for a better understanding of the mechanism of CT interaction between feeds. The present work was designed to measure, in vitro, the effects of CT in sainfoin when mixed with fresh lucerne
Environmental Spillovers and their Impacts on Housing Prices: A Spatial Hedonic Analysis
This paper investigates the spatial dimension of environmental factors on housing prices. We develop spatial hedonic models to estimate the implicit prices of various environmental attributes. The spatial dimension can be interpreted in terms of local or global spillovers. We conduct an empirical study in the Loire estuary (France). We focus on natural areas and more artificialized ones (ocean frontage, wetlands, rivers, and noisy roads). We show that, depending on the spatial model used, the implicit price is more than just the estimated coefficient value and combines both a feedback effect and a propagation effect
Onto what planes should Coulomb stress perturbations be resolved?
[1] Coulomb stress maps are produced by computing the tensorial stress perturbation due to an earthquake rupture and resolving this tensor onto planes of a particular orientation. It is often assumed that aftershock fault planes are ‘‘optimally oriented’’; in other words, the regional stress and coseismic stress change are used to compute the orientation of planes most likely to fail and the coseismic stress is resolved onto these orientations. This practice assumes that faults capable of sustaining aftershocks exist at all orientations, an assumption contradicted by the observation that aftershock focal mechanisms have strong preferred orientations consistent with mapped structural trends. Here we systematically investigate the best planes onto which stress should be resolved for the Landers, Hector Mine, Loma Prieta, and Northridge earthquakes by quantitatively comparing observed aftershock distributions with stress maps based on optimally oriented planes (two- and three-dimensional), main shock orientation, and regional structural trend. We find that the best model differs between different tectonic regions but that in all cases, models that incorporate the regional stress field tend to produce stress maps that best fit the observed aftershock distributions, although not all such models do so equally well. Our results suggest that when the regional stress field is poorly defined, or in structurally complex areas, the best model may be to fix the strike of the planes upon which the stress is to be resolved to that of the main shock but allow the dip and rake to vary
PHotometry Assisted Spectral Extraction (PHASE) and identification of SNLS supernovae
Aim: We present new extraction and identification techniques for supernova
(SN) spectra developed within the Supernova Legacy Survey (SNLS) collaboration.
Method: The new spectral extraction method takes full advantage of
photometric information from the Canada-France-Hawai telescope (CFHT) discovery
and reference images by tracing the exact position of the supernova and the
host signals on the spectrogram. When present, the host spatial profile is
measured on deep multi-band reference images and is used to model the host
contribution to the full (supernova + host) signal. The supernova is modelled
as a Gaussian function of width equal to the seeing. A chi-square minimisation
provides the flux of each component in each pixel of the 2D spectrogram. For a
host-supernova separation greater than <~ 1 pixel, the two components are
recovered separately and we do not use a spectral template in contrast to more
standard analyses. This new procedure permits a clean extraction of the
supernova separately from the host in about 70% of the 3rd year ESO/VLT spectra
of the SNLS. A new supernova identification method is also proposed. It uses
the SALT2 spectrophotometric template to combine the photometric and spectral
data. A galaxy template is allowed for spectra for which a separate extraction
of the supernova and the host was not possible.
Result: These new techniques have been tested against more standard
extraction and identification procedures. They permit a secure type and
redshift determination in about 80% of cases. The present paper illustrates
their performances on a few sample spectra.Comment: 27 pages, 18 Figures, 1 Table. Accepted for publication in A&
The effect of progenitor age and metallicity on luminosity and 56Ni yield in Type Ia supernovae
Timmes, Brown & Truran found that metallicity variations could theoretically
account for a 25% variation in the mass of 56Ni synthesized in Type Ia
supernovae (SNe Ia), and thus account for a large fraction of the scatter in
observed SN Ia luminosities. Higher-metallicity progenitors are more
neutron-rich, producing more stable burning products relative to radioactive
56Ni. We develop a new method for estimating bolometric luminosity and 56Ni
yield in SNe Ia and use it to test the theory with data from the Supernova
Legacy Survey. We find that the average 56Ni yield does drop in SNe Ia from
high metallicity environments, but the theory can only account for 7%--10% of
the dispersion in SN Ia 56Ni mass, and thus luminosity. This is because the
effect is dominant at metallicities significantly above solar, whereas we find
that SN hosts have predominantly subsolar or only moderately above-solar
metallicities. We also show that allowing for changes in O/Fe with the
metallicity [Fe/H] does not have a major effect on the theoretical prediction
of Timmes, Brown & Truran, so long as one is using the O/H as the independent
variable. Age may have a greater effect than metallicity -- we find that the
luminosity weighted age of the host galaxy is correlated with 56Ni yield, and
thus more massive progenitors give rise to more luminous explosions. This is
hard to understand if most SNe Ia explode when the primaries reach the
Chandrasekhar mass. Finally, we test the findings of Gallagher et al., that the
residuals of SNe Ia from the Hubble diagram are correlated with host galaxy
metallicity, and we find no such correlation.Comment: ApJ, accepted, 34 pages, 11 figures, apologies for one column format
-- necessary for the equation
Photometric selection of high-redshift type Ia supernovae
We present a method for selecting high-redshift type Ia supernovae (SNe Ia)
located via rolling SN searches. The technique, using both color and magnitude
information of events from only 2-3 epochs of multi-band real-time photometry,
is able to discriminate between SNe Ia and core collapse SNe. Furthermore, for
the SNe Ia, the method accurately predicts the redshift, phase and light-curve
parameterization of these events based only on pre-maximum-light data. We
demonstrate the effectiveness of the technique on a simulated survey of SNe Ia
and core-collapse SNe, where the selection method effectively rejects most
core-collapse SNe while retaining SNe Ia. We also apply the selection code to
real-time data acquired as part of the Canada-France-Hawaii Telescope Supernova
Legacy Survey (SNLS). During the period May 2004 to January 2005 in the SNLS,
440 SN candidates were discovered of which 70 were confirmed spectroscopically
as SNe Ia and 15 as core-collapse events. For this test dataset, the selection
technique correctly identifies 100% of the identified SNe II as non-SNe Ia with
only a 1-2% false rejection rate. The predicted parameterization of the SNe Ia
has a precision of |delta_z|/(1+z_spec)<0.09 in redshift, and +/- 2-3
rest-frame days in phase, providing invaluable information for planning
spectroscopic follow-up observations. We also investigate any bias introduced
by this selection method on the ability of surveys such as SNLS to measure
cosmological parameters (e.g., w and omega matter), and find any effect to be
negligible.Comment: Accepted for publication in A
Comparison of LASSO and GPS time transfers
The LASSO is a technique which should allow the comparison of remote atomic clocks with sub-nanosecond precision and accuracy. The first successful time transfer using LASSO has been carried out between the Observatoire de la Cote d'Azur in France and the McDonald Observatory in Texas, United States. This paper presents a preliminary comparison of LASSO time transfer with GPS common-view time transfer
Type Ia Supernovae Rates and Galaxy Clustering from the CFHT Supernova Legacy Survey
The Canada-France-Hawaii Telescope Supernova Legacy Survey (SNLS) has created
a large homogeneous database of intermediate redshift (0.2 < z < 1.0) type Ia
supernovae (SNe Ia). The SNLS team has shown that correlations exist between SN
Ia rates, properties, and host galaxy star formation rates. The SNLS SN Ia
database has now been combined with a photometric redshift galaxy catalog and
an optical galaxy cluster catalog to investigate the possible influence of
galaxy clustering on the SN Ia rate, over and above the expected effect due to
the dependence of SFR on clustering through the morphology-density relation. We
identify three cluster SNe Ia, plus three additional possible cluster SNe Ia,
and find the SN Ia rate per unit mass in clusters at intermediate redshifts is
consistent with the rate per unit mass in field early-type galaxies and the SN
Ia cluster rate from low redshift cluster targeted surveys. We also find the
number of SNe Ia in cluster environments to be within a factor of two of
expectations from the two component SNIa rate model.Comment: 21 pages, 2 figures, 6 tables, accepted for publication in A
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