13,216 research outputs found
The Supernova Legacy Survey 3-year sample: Type Ia supernovae photometric distances and cosmological constraints
Aims. We present photometric properties and distance measurements of 252 high redshift Type Ia supernovae (0.15 < z < 1.1)
discovered during the first three years of the Supernova Legacy Survey (SNLS). These events were detected and their multi-colour
light curves measured using the MegaPrime/MegaCam instrument at the Canada-France-Hawaii Telescope (CFHT), by repeatedly
imaging four one-square degree fields in four bands. Follow-up spectroscopy was performed at the VLT, Gemini and Keck telescopes
to confirm the nature of the supernovae and to measure their redshifts.
Methods. Systematic uncertainties arising from light curve modeling are studied, making use of two techniques to derive the peak
magnitude, shape and colour of the supernovae, and taking advantage of a precise calibration of the SNLS fields.
Results. A flat ÎCDM cosmological fit to 231 SNLS high redshift type Ia supernovae alone gives Ω_M = 0.211 ± 0.034(stat) ±
0.069(sys). The dominant systematic uncertainty comes from uncertainties in the photometric calibration. Systematic uncertainties
from light curve fitters come next with a total contribution of ± 0.026 on Ω_M. No clear evidence is found for a possible evolution of
the slope (ÎČ) of the colour-luminosity relation with redshift
Shear effects in lateral piezoresponse force microscopy at 180 ferroelectric domain walls
In studies using piezoresponse force microscopy, we observe a non-zero
lateral piezoresponse at 180 domain walls in out-of-plane polarized,
c-axis-oriented tetragonal ferroelectric Pb(ZrTi)O
epitaxial thin films. We attribute these observations to a shear strain effect
linked to the sign change of the piezoelectric coefficient through the
domain wall, in agreement with theoretical predictions. We show that in
monoclinically distorted tetragonal BiFeO films, this effect is
superimposed on the lateral piezoresponse due to actual in-plane polarization,
and has to be taken into account in order to correctly interpret the
ferroelectric domain configuration.Comment: 4 pages, 3 figure
Comparaison des qualitĂ©s sensorielles de la viande et de la carcasse dâagneaux Ă©levĂ©s au pĂąturage en production biologique ou conventionnelle Ă deux niveaux de disponibilitĂ©s en herbe
Nous avons comparĂ© les qualitĂ©s sensorielles des carcasses et des viandes dâagneaux engraissĂ©s au pĂąturage en Ă©levage biologique ou conventionnel (O vs. C) Ă deux niveaux de disponibilitĂ©s en herbe (Haut H vs. Bas L). Le profil de croissance a Ă©tĂ© maintenu similaire entre les deux systĂšmes de production. LâexpĂ©rimentation a Ă©tĂ© conduite pendant deux annĂ©es avec 12 agneaux mĂąles castrĂ©s de race Limousine dans chaque groupe OH, OL, CH et CL chaque annĂ©e. Les traitements O et C diffĂ©raient par le niveau de fertilisation azotĂ©e minĂ©rale Ă©pandu sur les parcelles. Les parcelles expĂ©rimentales Ă©taient des repousses aprĂšs fauche et elles Ă©taient conduites en pĂąturage tournant pour conduire Ă un Ăąge moyen des agneaux Ă lâabattage de 5 et 6 mois dans les lots H et L respectivement. Les cĂŽtelettes O ont Ă©tĂ© moins apprĂ©ciĂ©es que les cĂŽtelettes C. Lâindice de rouge du muscle longissimus thoracis et lumborum aprĂšs 2h dâexposition Ă lâair a Ă©tĂ© plus Ă©levĂ© chez les agneaux L que chez les agneaux H, indiquant les effets possibles dâune intensification de lâĂ©levage biologique Ă travers une augmentation du chargement
Changing the Scaling Relation: The Need For a Mean Molecular Weight Term
The scaling relations that relate the average asteroseismic parameters
and to the global properties of stars are used quite
extensively to determine stellar properties. While the scaling
relation has been examined carefully and the deviations from the relation have
been well documented, the scaling relation has not been examined
as extensively. In this paper we examine the scaling relation
using a set of stellar models constructed to have a wide range of mass,
metallicity, and age. We find that as with , does not
follow the simple scaling relation. The most visible deviation is because of a
mean molecular weight term and a term that are commonly ignored. The
remaining deviation is more difficult to address. We find that the influence of
the scaling relation errors on asteroseismically derived values of are
well within uncertainties. The influence of the errors on mass and radius
estimates is small for main sequence and subgiants, but can be quite large for
red giants.Comment: 15 pages, 14 figures, accepted for publication in Ap
Thermal design and analysis of a hydrogen-burning wind tunnel model of an airframe-integrated scramjet
An aerodynamic model of a hydrogen burning, airframe integrated scramjet engine has been designed, fabricated, and instrumented. This model is to be tested in an electric arc heated wind tunnel at an altitude of 35.39 km (116,094 ft.) but with an inlet Mach number of 6 simulating precompression on an aircraft undersurface. The scramjet model is constructed from oxygen free, high conductivity copper and is a heat sink design except for water cooling in some critical locations. The model is instrumented for pressure, surface temperature, heat transfer rate, and thrust measurements. Calculated flow properties, heat transfer rates, and surface temperature distributions along the various engine components are included for the conditions stated above. For some components, estimates of thermal strain are presented which indicate significant reductions in plastic strain by selective cooling of the model. These results show that the 100 thermal cycle life of the engine was met with minimum distortion while staying within the 2669 N (600 lbf) engine weight limitation and while cooling the engine only in critical locations
Determination of the critical current density in the d-wave superconductor YBCO under applied magnetic fields by nodal tunneling
We have studied nodal tunneling into YBa2Cu3O7-x (YBCO) films under magnetic
fields. The films' orientation was such that the CuO2 planes were perpendicular
to the surface with the a and b axis at 450 form the normal. The magnetic field
was applied parallel to the surface and perpendicular to the CuO2 planes. The
Zero Bias Conductance Peak (ZBCP) characteristic of nodal tunneling splits
under the effect of surface currents produced by the applied fields. Measuring
this splitting under different field conditions, zero field cooled and field
cooled, reveals that these currents have different origins. By comparing the
field cooled ZBCP splitting to that taken in decreasing fields we deduce a
value of the Bean critical current superfluid velocity, and calculate a Bean
critical current density of up to 3*10^7 A/cm2 at low temperatures. This
tunneling method for the determination of critical currents under magnetic
fields has serious advantages over the conventional one, as it avoids having to
make high current contacts to the sample.Comment: 8 pages, 2 figure
Is there Evidence for a Hubble bubble? The Nature of Type Ia Supernova Colors and Dust in External Galaxies
We examine recent evidence from the luminosity-redshift relation of Type Ia
Supernovae (SNe Ia) for the detection of a ``Hubble bubble'' --
a departure of the local value of the Hubble constant from its globally
averaged value \citep{Jha:07}. By comparing the MLCS2k2 fits used in that study
to the results from other light-curve fitters applied to the same data, we
demonstrate that this is related to the interpretation of SN color excesses
(after correction for a light-curve shape-color relation) and the presence of a
color gradient across the local sample. If the slope of the linear relation
() between SN color excess and luminosity is fit empirically, then the
bubble disappears. If, on the other hand, the color excess arises purely from
Milky Way-like dust, then SN data clearly favors a Hubble bubble. We
demonstrate that SN data give , instead of the
one would expect from purely Milky-Way-like dust. This suggests that either SN
intrinsic colors are more complicated than can be described with a single
light-curve shape parameter, or that dust around SN is unusual. Disentangling
these possibilities is both a challenge and an opportunity for large-survey SN
Ia cosmology.Comment: Further information and data at
http://qold.astro.utoronto.ca/conley/bubble/ Accepted for publication in ApJ
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