33,953 research outputs found
Application of the Contouring Method to Extended Microlensed Sources
The method devised by Lewis et al. (1993) for calculating the light curve of
a microlensed point source is expanded to two dimensions to enable the
calculation of light curves of extended sources. This method is significantly
faster than the ray shooting method that has been used in the past. The
increased efficiency is used to obtain much higher resolution light curves over
increased timescales. We investigate the signatures arising from different
source geometries in a realistic microlensing model. We show that a large
fraction of high magnification events (HMEs) in image A of Q2237+0305 involve
only one caustic, and could therefore yield information on the structure of the
quasar continuum through the recognition of a characteristic event shape. In
addition, the cataloguing of HMEs into morphological type will, in theory,
enable the direction of the transverse motion, as well as the source size to be
obtained from long term monitoring.Comment: 10 pages including 4 figures. Accepted for publication in M.N.R.A.
X-Shooting EF Eridani: further evidence for a massive white dwarf and a sub-stellar secondary
High resolution spectral observations of the polar EF Eridani obtained in a
low state with X-Shooter revealed narrow emission lines from the irradiated
secondary. The lines were most prominent in the near-IR Ca2-triplet, the more
intensive Halpha line had additional emission likely originating from an
accretion stream. The lines with a radial velocity amplitude, K2' = 385 +- 4
kmps, serve as tracer of the otherwise unseen companion. The mass function
implies a massive white dwarf with Mwd > 0.65 Msun at 3sigma confidence, and a
short distance to the binary, d ~ 111 pc (<145pc at 3sigma confidence). The
spectral energy distribution from the UV to the IR together with the high mass
ratio gives further strong evidence of EF Eri being a post period-minimum
object with M2 < 0.06 MsunComment: Astron, Astrophys., in pres
Freeze-Thaw Durability and Long-Term Performance Evaluation of Shotcrete in Cold Regions
This study’s aim was to evaluate the freeze-thaw durability of shotcrete in cold regions and predict its long-term performance. One benchmark mix design from the WSDOT was chosen to prepare samples for performance evaluation. Shotcrete specimens were conditioned in accordance with ASTM C666. The long-term freeze-thaw performance after certain cycles was evaluated using the dynamic modulus of elasticity test (ASTM C215), fracture energy test (RILEM 50-FMC), and X-ray CT microstructure imaging analysis. Probabilistic damage analysis was conducted to establish the relation between the durability life and the damage parameter for different probabilities of reliability using the three-parameter Weibull distribution model. The fracture energy test was found to be a more sensitive test method than the dynamic modulus of elasticity for screening material deterioration over time and for capturing accumulative material damage caused by rapid freeze-thaw action, because of smaller durability factors (degradation ratios) obtained from the fracture energy test. X-ray CT imaging analysis is capable of detecting microcracks that form and pore evolution in the aggregate and interface transition zone of conditioned samples. Moreover, the continuum damage mechanic-based model shows potential in predicting long-term material degradation and the service life of shotcrete
A kinematical approach to gravitational lensing using new formulae for refractive index and acceleration
This paper uses the Schwarzschild metric to derive an effective refractive
index and acceleration vector that account for relativistic deflection of light
rays, in an otherwise classical kinematic framework. The new refractive index
and the known path equation are integrated to give accurate results for travel
time and deflection angle, respectively. A new formula for coordinate
acceleration is derived which describes the path of a massless test particle in
the vicinity of a spherically symmetric mass density distribution. A standard
ray-shooting technique is used to compare the deflection angle and time delay
predicted by this new formula with the previously calculated values, and with
standard first order approximations. Finally, the ray shooting method is used
in theoretical examples of strong and weak lensing, reproducing known
observer-plane caustic patterns for multiple masses.Comment: 11 pages, 7 figures, MNRAS accepte
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