1,206 research outputs found
Endogenous Lobbying
In this paper we endogenize the number and characteristics of lobbies in a citizen-candidate model of representative democracy where citizens can lobby an elected policy-maker. We find that lobbying always matters. That is, lobbying always affects equilibrium policy outcomes. Moreover, only one policy outcome emerges in equilibrium. An "extremist" candidate is elected and implements a "centrist" policy that differs from the one most preferred by the median voter. These results are in contrast with the ones obtained in the context of a citizen-candidate model where lobbies are exogenous.Lobbying, citizen-candidate, representative democracy, electoral competition
Time decay of scaling invariant Schroedinger equations on the plane
We prove the sharp L^1-L^{\infty} time-decay estimate for the 2D-Schroedinger
equation with a general family of scaling critical electromagnetic potentials.Comment: 26 page
Massive Protoplanetary Disks in the Trapezium Region
(abridged) We determine the disk mass distribution around 336 stars in the
young Orion Nebula cluster by imaging a 2.5' x 2.5' region in 3 mm continuum
emission with the Owens Valley Millimeter Array. For this sample of 336 stars,
we observe 3 mm emission above the 3-sigma noise level toward ten sources, six
of which have also been detected optically in silhouette against the bright
nebular background. In addition, we detect 20 objects that do not correspond to
known near-IR cluster members. Comparisons of our measured fluxes with longer
wavelength observations enable rough separation of dust emission from thermal
free-free emission, and we find substantial dust emission toward most objects.
For the ten objects detected at both 3 mm and near-IR wavelengths, eight
exhibit substantial dust emission. Excluding the high-mass stars and assuming a
gas-to-dust ratio of 100, we estimate circumstellar masses ranging from 0.13 to
0.39 Msun. For the cluster members not detected at 3 mm, images of individual
objects are stacked to constrain the mean 3 mm flux of the ensemble. The
average flux is detected at the 3-sigma confidence level, and implies an
average disk mass of 0.005 Msun, comparable to the minimum mass solar nebula.
The percentage of stars in Orion surrounded by disks more massive than ~0.1
Msun is consistent with the disk mass distribution in Taurus, and we argue that
massive disks in Orion do not appear to be truncated through close encounters
with high-mass stars. Comparison of the average disk mass and number of massive
dusty structures in Orion with similar surveys of the NGC 2024 and IC 348
clusters constrains the evolutionary timescales of massive circumstellar disks
in clustered environments.Comment: 27 pages, including 7 figures. Accepted by Ap
New signposts of massive star formation in the S235A-B region
We report on new aspects of the star-forming region S235AB revealed through
high-resolution observations at radio and mid-infrared wavelengths. Using the
Very Large Array, we carried out sensitive observations of S235AB in the cm
continuum (6, 3.6, 1.3, and 0.7) and in the 22 GHz water maser line. These were
complemented with Spitzer Space Telescope Infrared Array Camera archive data to
clarify the correspondence between radio and IR sources. We made also use of
newly presented data from the Medicina water maser patrol, started in 1987, to
study the variability of the water masers found in the region. S235A is a
classical HII region whose structure is now well resolved. To the south, no
radio continuum emission is detected either from the compact molecular core or
from the jet-like structure observed at 3.3 mm, suggesting emission from dust
in both cases. We find two new compact radio continuum sources (VLA-1 and
VLA-2) and three separate maser spots. VLA-1 coincides with one of the maser
spots and with a previously identified IR source (M1). VLA-2 lies towards S235B
and represents the first radio detection from this peculiar nebula that may
represent an ionized wind from a more evolved star. The two other maser spots
coincide with an elongated structure previously observed within the molecular
core in the C34S line. This structure is perpendicular to a bipolar molecular
outflow observed in HCO+(1-0) and may trace the associated equatorial disk. The
Spitzer images reveal a red object towards the molecular core. This is the most
viable candidate for the embedded source originating the outflow and maser
phenomenology. The picture emerging from these and previous data shows the
extreme complexity of a small (< 0.5 pc) star-forming region where widely
different stages of stellar evolution are present.Comment: 15 pages, 16 figures, to be published in Astronomy & Astrophysic
A 1.3 cm wavelength radio flare from a deeply embedded source in the Orion BN/KL region
Aims: Our aim was to measure and characterize the short-wavelength radio
emission from young stellar objects (YSOs) in the Orion Nebula Cluster and the
BN/KL star-forming region. Methods: We used the NRAO Very Large Array at a
wavelength of 1.3 cm and we studied archival X-ray, infrared, and radio data.
Results: During our observation, a strong outburst (flux increasing >10 fold)
occurred in one of the 16 sources detected at a wavelength of 1.3cm, while the
others remained (nearly) constant. This source does not have an infrared
counterpart, but has subsequently been observed to flare in X-rays. Curiously,
a very weak variable double radio source was found at other epochs near this
position, one of whose components is coincident with it. A very high extinction
derived from modeling the X-ray emission and the absence of an infrared
counterpart both suggest that this source is very deeply embedded.Comment: 7 pages, 5 figures, accepted for publication in A&
An Alternative to Spinning Dust for the Microwave Emission of LPH 201.663+1.643: an Ultracompact HII Region
The microwave spectral energy distribution of the dusty, diffuse H II region
LPH 201.663+1.643 has been interpreted by others as tentative evidence for
microwave emission from spinning dust grains. We present an alternative
interpretation for that particular object; specifically, that an ultracompact H
II region embedded within the dust cloud would explain the available
observations as well or better than spinning dust. Parameters for the size,
surface brightness, and flux density of the putative ultracompact HII region,
derived from the microwave observations, are within known ranges. A possible
candidate for such an ultracompact H II region is IRAS 06337+1051, based upon
its infrared colors. However, IRAS 06337+1051's infrared flux appears to be too
small to be consistent with the microwave flux required for this alternative
model to explain the observations.Comment: 11 pages, 3 figures, accepted to ApJ Letter
A Parallactic Distance of 389 +24/-21 parsecs to the Orion Nebula Cluster from Very Long Baseline Array Observations
We determine the parallax and proper motion of the flaring, non-thermal radio
star GMR A, a member of the Orion Nebula Cluster, using Very Long Baseline
Array observations. Based on the parallax, we measure a distance of 389 +24/-21
parsecs to the source. Our measurement places the Orion Nebula Cluster
considerably closer than the canonical distance of 480 +/- 80 parsecs
determined by Genzel et al. (1981). A change of this magnitude in distance
lowers the luminosities of the stars in the cluster by a factor of ~ 1.5. We
briefly discuss two effects of this change--an increase in the age spread of
the pre-main sequence stars and better agreement between the zero-age
main-sequence and the temperatures and luminosities of massive stars.Comment: 10 pages, 4 figures, emulateapj, accepted to Ap
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