4,640 research outputs found
Evaluation of Cracking Behavior of Cold In-Place Recycling Asphalt Mixtures
During the last decades, the asphalt pavement industry has been looking for innovative ways to make its products more environmentally friendly, and recycling methodologies have become widely accepted. According to the National Asphalt Pavement Association, during 2017 construction season, more than 76.2 million tons of RAP were put to use in new pavements in the United States, saving taxpayers more than $2.2 billion. [1]Recycling of the existing deteriorated asphalt pavement offers an attractive approach from the economic and structural standpoint. However, a severely cracked asphalt pavement presents a challenge for the design engineer due to the uncertainty in its cracking behavior and its potential of reflecting the cracks through the new overlay. The Cold In-place Recycling technique has demonstrated effectiveness in delaying the problem of reflective cracking and providing strong base layer, resulting in the requirement of a thinner overlay [2] [3] [4].This study evaluated the cracking properties of CIR by means of the Overlay Tester (OT) and the Flexural Beam Fatigue Test. The results indicated that CIR materials have good (low) crack propagation rates but the required energy to initiate a crack is low as well. In addition, some flexibility was observed in the Beam Fatigue Test but a stiff-brittle behavior was predominant. The performance characteristics of the CIR materials were used in a mechanistic analysis to recommend a structural layer coefficient for CIR layer in a flexible pavement structure
Caracterización del Comercio de Fauna Acuática Exótica en Republica Dominicana Durante el Periodo 2006 - 2010
Variable stars in the Fornax dSph Galaxy. II. Pulsating stars below the horizontal branch
We have carried out an intensive survey of the northern region of the Fornax
dwarf spheroidal galaxy with the aim of detecting the galaxy's short--period
pulsating stars (P<0.25 days). Observations collected over three consecutive
nights with the Wide Field Imager of the 2.2m MPI telescope at ESO allowed us
to detect 85 high-amplitude (0.20-1.00 mag in B-light) variable stars with
periods in the range from 0.046 to 0.126 days, similar to SX Phoenicis stars in
Galactic metal-poor stellar populations. The plots of the observed periods vs.
the B and V magnitudes show a dispersion largely exceeding the observational
errors. To disentangle the matter, we separated the first-overtone from the
fundamental-mode pulsators and tentatively identified a group of subluminous
variables, about 0.35 mag fainter than the others. Their nature as either
metal-poor intermediate-age stars or stars formed by the merging of close
binary systems is discussed. The rich sample of the Fornax variables also led
us to reconstruct the Period-Luminosity relation for short-period pulsating
stars. An excellent linear fit, M(V)=-1.83(+/-0.08)-3.65(+/-0.07) log P(fund),
was obtained using 153 Delta Scuti and SX Phoenicis stars in a number of
different stellar systems.Comment: 11 pages plus 1 on-line figure and 1 on-line table; accepted for
publication in ApJ. Part of this work has been the subject of the Laurea
thesis of LDA. His supervisor and our colleague, Prof. Laura E. Pasinetti,
suddendly passed away on September 13, 2006. Several astronomers have been
trained under her tutelage and we gratefully honor her memor
The Velocity Dispersion Profile of the Remote Dwarf Spheroidal Galaxy Leo I: A Tidal Hit and Run?
(abridged) We present kinematic results for a sample of 387 stars located
near Leo I based on spectra obtained with the MMT's Hectochelle spectrograph
near the MgI/Mgb lines. We estimate the mean velocity error of our sample to be
2.4 km/s, with a systematic error of < 1 km/s. We produce a final sample of 328
Leo I red giant members, from which we measure a mean heliocentric radial
velocity of 282.9 +/- 0.5 km/s, and a mean radial velocity dispersion of 9.2
+/- 0.4 km/s for Leo I. The dispersion profile of Leo I is flat out to beyond
its classical `tidal' radius. We fit the profile to a variety of equilibrium
dynamical models and can strongly rule out models where mass follows light.
Two-component Sersic+NFW models with tangentially anisotropic velocity
distributions fit the dispersion profile well, with isotropic models ruled out
at a 95% confidence level. The mass and V-band mass-to-light ratio of Leo I
estimated from equilibrium models are in the ranges 5-7 x 10^7 M_sun and 9-14
(solar units), respectively, out to 1 kpc from the galaxy center. Leo I members
located outside a `break radius' (about 400 arcsec = 500 pc) exhibit
significant velocity anisotropy, whereas stars interior appear to have
isotropic kinematics. We propose the break radius represents the location of
the tidal radius of Leo I at perigalacticon of a highly elliptical orbit. Our
scenario can account for the complex star formation history of Leo I, the
presence of population segregation within the galaxy, and Leo I's large outward
velocity from the Milky Way. The lack of extended tidal arms in Leo I suggests
the galaxy has experienced only one perigalactic passage with the Milky Way,
implying that Leo I may have been injected into its present orbit by a third
body a few Gyr before perigalacticon.Comment: ApJ accepted, 23 figures, access paper as a pdf file at
http://www.astro.lsa.umich.edu/~mmateo/research.htm
HST Studies of the WLM Galaxy. I. The Age and Metallicity of the Globular Cluster
We have obtained V and I images of the lone globular cluster that belongs to
the dwarf Local Group irregular galaxy known as WLM. The color-magnitude
diagram of the cluster shows that it is a normal old globular cluster with a
well-defined giant branch reaching to M_V=-2.5, a horizontal branch at
M_V=+0.5, and a sub-giant branch extending to our photometry limit of M_V=+2.0.
A best fit to theoretical isochrones indicates that this cluster has a
metallicity of [Fe/H]=-1.52\pm0.08 and an age of 14.8\pm0.6 Gyr, thus
indicating that it is similar to normal old halo globulars in our Galaxy. From
the fit we also find that the distance modulus of the cluster is 24.73\pm0.07
and the extinction is A_V=0.07\pm0.06, both values that agree within the errors
with data obtained for the galaxy itself by others. We conclude that this
normal massive cluster was able to form during the formation of WLM, despite
the parent galaxy's very small intrinsic mass and size.Comment: 14 pages, 5 figures, 1 tabl
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