576 research outputs found
Embodied technical change in a two-sector AK model
In this paper, we study a two-sector version of the AK model proposed by Rebelo (1991), where constant returns to capital are confined to the investment goods sector. We show that this setup, an endogenous growth extension to the model of Greenwood, Hercowitz, and Krusell (1997), reproduces important features of the U.S. NIPA data, namely the secular downward trend of the price of equipment investment relative to non- durable consumption and the increasing ratio of real equipment investment to real output. The main difference to the one-sector AK model lies in the existence of obsolescence costs, which decrease output growth if the elasticity of intertemporal substitution is larger than the saving rate.subliminal extant Smith economagic gmm
Rotationally resolved spectroscopy of dwarf planet (136472) Makemake
Context. Icy dwarf planets are key for studying the chemical and physical
states of ices in the outer solar system. The study of secular and rotational
variations gives us hints of the processes that contribute to the evolution of
their surface. Aims. The aim of this work is to search for rotational
variability on the surface composition of the dwarf planet (136472) Makemake
Methods. We observed Makemake in April 2008 with the medium-resolution
spectrograph ISIS, at the William Herschel Telescope (La Palma, Spain) and
obtained a set of spectra in the 0.28 - 0.52 {\mu}m and 0.70 - 0.95 {\mu}m
ranges, covering 82% of its rotational period. For the rotational analysis, we
organized the spectra in four different sets corresponding to different
rotational phases, and after discarding one with low signal to noise, we
analyzed three of them that cover 71% of the surface. For these spectra we
computed the spectral slope and compared the observed spectral bands of methane
ice with reflectances of pure methane ice to search for shifts of the center of
the bands, related to the presence of CH 4 /N 2 solid solution. Results. All
the spectra have a red color with spectral slopes between 20%/1000 {\AA} and
32%/1000 {\AA} in accordance with previously reported values. Some variation in
the spectral slope is detected, pointing to the possibility of a variation in
the surface content or the particle size of the solid organic compound. The
absorption bands of methane ice present a shift toward shorter wavelengths,
indicating that methane (at least partially) is in solid solution with
nitrogen. There is no variation within the errors of the shifts with the
wavelength or with the depth of the bands, so there is no evidence of variation
in the CH 4 /N 2 mixing ratio with rotation. By comparing with all the
available data in the literature, no secular compositional variations between
2005 and 2008 is found
Dust loss from activated asteroid P/2015 X6
We present observations and dust tail models of activated asteroid P/2015 X6
from deep imaging data acquired at the 10.4m Gran Telescopio Canarias (GTC)
from mid-December 2015 to late January 2016. The results of the modeling
indicate that the asteroid has undergone a sustained dust loss over a two-month
or longer period. The dust parameters, derived from multidimensional fits of
the available images, are compatible with either ice sublimation or rotational
instability processes. An impulsive event, as it could be associated to an
impact with another body, is less likely. A power-law distribution of
particles, with minimum and maximum radius of 1 m and 1 cm, and power
index of --3.3 is found to be consistent with the observations. Depending on
the ejection velocity model adopted, the particle velocities are found in the
0.3 to 10 m s range. The activation time was between 18-26 days before
discovery. The total ejected mass from that time to the most recent observation
is in the range 5-910 kg. No dust features giving indication of
past activity earlier than the activation time have been observed.Comment: Accepted by ApJ, May 15th 201
On the dust environment of Main-Belt Comet 313P/Gibbs
We present observations carried out using the 10.4 m Gran Telescopio Canarias
and an interpretative model of the dust environment of activated asteroid
313P/Gibbs. We discuss three different models relating to different values of
the dust parameters, i.e, dust loss rate, maximum and minimum sizes of
particles, power index of the size distribution, and emission pattern. The best
model corresponds with an isotropic emission of particles which started on
August 1st. The size of grains were in the range of m, with
velocities for 100 m particles between ms, with a dust
production rate in the range of kgs. The dust tails'
brightness and morphology are best interpreted in terms of a model of sustained
and low dust emission driven by water-ice sublimation, spanning since 2014
August 1st, and triggered by a short impulsive event. This event produced an
emission of small particles of about 0.1 m with velocities of 4
ms. From our model we deduce that the activity of this Main-Belt
Comet continued for, at least, four months, since activation.Comment: 14 pages, 4 figures, 2 tables. Accepted for publication in The
Astrophysical Journa
Near-infrared spectroscopy of 1999 JU3, the target of the Hayabusa 2 mission
Context. Primitive asteroids contain complex organic material and ices
relevant to the origin of life on Earth. These types of asteroids are the
target of several-sample return missions to be launched in the next years. 1999
JU3 is the target of the Japanese Aerospace Exploration Agency's Hayabusa 2
mission. Aims. 1999 JU3 has been previously identified as a C-class asteroid.
Spectroscopic observations at longer wavelengths will help to constrain its
composition. Methods. We obtained spectroscopy of 1999 JU3 from 0.85 to 2.2
microns, with the 3.6 m Telescopio Nazionale Galileo using the low resolution
mode of the Near Infrared Camera Spectrograph. Results. We present a
near-infrared spectrum of 1999 JU3 from 0.85 to 2.2microns that is consistent
with previously published spectra and with its C-type classification.
Conclusions. Our spectrum confirms the primitive nature of 1999 JU3 and its
interest as target of the sample-return mission Hayabusa 2.Comment: Research Note: 3 pages 1 Figure Received December 2012; accepted 4
March 201
Early evolution of disrupted asteroid P/2016 G1 (PANSTARRS)
We present deep imaging observations of activated asteroid P/2016 G1
(PANSTARRS) using the 10.4m Gran Telescopio Canarias (GTC) from late April to
early June 2016. The images are best interpreted as the result of a relatively
short-duration event with onset about days before
perihelion (i.e., around 10th February, 2016), starting sharply and decreasing
with a days (Half-width at half-maximum, HWHM). The
results of the modeling imply the emission of 1.710 kg of
dust, if composed of particles of 1 micrometer to 1 cm in radius, distributed
following a power-law of index --3, and having a geometric albedo of 0.15. A
detailed fitting of a conspicuous westward feature in the head of the
comet-like object indicates that a significant fraction of the dust was ejected
along a privileged direction right at the beginning of the event, which
suggests that the parent body has possibly suffered an impact followed by a
partial or total disruption. From the limiting magnitude reachable with the
instrumental setup, and assuming a geometric albedo of 0.15 for the parent
body, an upper limit for the size of possible fragment debris of 50 m in
radius is derived.Comment: Accepted by ApJ Letter
Thermophysical properties of near-Earth asteroid (341843) 2008 EV5 from WISE data
Aims. To derive the thermal inertia of 2008 EV, the baseline target for
the Marco Polo-R mission proposal, and infer information about the size of the
particles on its surface. Methods. Values of thermal inertia are obtained by
fitting an asteroid thermophysical model to NASA's Wide-field Infrared Survey
Explorer (WISE) infrared data. From the constrained thermal inertia and a model
of heat conductivity that accounts for different values of the packing fraction
(a measure of the degree of compaction of the regolith particles), grain size
is derived. Results. We obtain an effective diameter , geometric visible albedo (assuming
), and thermal inertia J/m2/s(1/2)/K at
the 1- level of significance for its retrograde spin pole solution. The
regolith particles radius is mm for low degrees of
compaction, and mm for the highest packing densities.Comment: 16 pages, 8 figures; accepted for publication in Astronomy &
Astrophysic
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