4,993 research outputs found
Do Campaign Contribution Limits Curb the Influence of Money in Politics?
Over 40% of countries around the world have adopted limits on campaign contributions to curb the influence of money in politics. Yet, we have limited knowledge on whether and how these limits achieve this goal. With a regression discontinuity design that uses institutional rules on contribution limits in Colombian municipalities, we show that looser limits increase the number and value of public contracts assigned to the winning candidateâs donors. The evidence suggests that this is explained by looser limits concentrating influence over the elected candidate among top donors and not by a reduction in electoral competition or changes in who runs for office. We further show that looser limits worsen the performance of donor-managed contracts: they are more likely to run over costs and require time extensions. Overall, this paper demonstrates a direct link between campaign contribution limits, donor kickbacks, and worse government contract performance
Grain Sorghum Response to Band Applied Zinc Fertilizer
Zinc (Zn) is one of the micronutrients found to be deficient in Kansas. The objective of this study was to evaluate the response of grain sorghum to Zn fertilization using strip trials. The experiment was set up in Manhattan, KS, in 2015. The experimental design consisted of two strips, one with Zn fertilizer and the other without, with five replications. Zn fertilizer was applied as starter in combination with ammonium polyphosphate at the rate of 0.5 lb Zn/a. Plant tissue samples were collected to determine Zn content. Grain yield was recorded by combine equipped with yield monitor. No significant differences were found for sorghum grain yield. Grain Zn content increased with Zn fertilization. Zn fertilization may be considered for future studies in food biofortification
Calibration of semi-analytic models of galaxy formation using Particle Swarm Optimization
We present a fast and accurate method to select an optimal set of parameters
in semi-analytic models of galaxy formation and evolution (SAMs). Our approach
compares the results of a model against a set of observables applying a
stochastic technique called Particle Swarm Optimization (PSO), a self-learning
algorithm for localizing regions of maximum likelihood in multidimensional
spaces that outperforms traditional sampling methods in terms of computational
cost. We apply the PSO technique to the SAG semi-analytic model combined with
merger trees extracted from a standard CDM N-body simulation. The
calibration is performed using a combination of observed galaxy properties as
constraints, including the local stellar mass function and the black hole to
bulge mass relation. We test the ability of the PSO algorithm to find the best
set of free parameters of the model by comparing the results with those
obtained using a MCMC exploration. Both methods find the same maximum
likelihood region, however the PSO method requires one order of magnitude less
evaluations. This new approach allows a fast estimation of the best-fitting
parameter set in multidimensional spaces, providing a practical tool to test
the consequences of including other astrophysical processes in SAMs.Comment: 11 pages, 4 figures, 1 table. Accepted for publication in ApJ.
Comments are welcom
A Kinematic Model for the Narrow-Line Region in NGC 4151
We present a simple kinematic model for the narrow-line region (NLR) of the
Seyfert 1 galaxy NGC 4151, based on our previous observations of extended [O
III] emission with the Space Telescope Imaging Spectrograph (STIS). The model
is similar to a biconical radial outflow model developed for the Seyfert 2
galaxy NGC 1068, except that the bicone axis is tilted much more into our line
of sight (40 degrees out of the plane of the sky instead of 5 degrees), and the
maximum space velocities are lower (750 km/s instead of 1300 km/s. We find
evidence for radial acceleration of the emission-line knots to a distance of
160 pc, followed by deceleration that approaches the systemic velocity at a
distance of 290 pc (for a distance to NGC 4151 of 13.3 Mpc). Other similarities
to the kinematics of NGC 1068 are: 1) there are a number of high-velocity
clouds that are not decelerated, suggesting that the medium responsible for the
deceleration is patchy, and 2) the bicone in NGC 4151 is at least partially
evacuated along its axis. Together, these two Seyfert galaxies provide strong
evidence for radial outflow (e.g., due to radiation and/or wind pressure) and
against gravitational motion or expansion away from the radio jets as the
principal kinematic component in the NLR.Comment: 31 pages, Latex, includes 11 figures in postscript, Figures
5a,5b,6a,6b in color, to appear in the Astronomical Journa
Properties of Submillimeter Galaxies in a Semi-analytic Model using the "Count Matching" Approach: Application to the ECDF-S
We present a new technique for modeling submillimeter galaxies (SMGs): the
"Count Matching" approach. Using lightcones drawn from a semi-analytic model of
galaxy formation, we choose physical galaxy properties given by the model as
proxies for their submillimeter luminosities, assuming a monotonic
relationship. As recent interferometric observations of the Extended Chandra
Deep Field South show that the brightest sources detected by single-dish
telescopes are comprised by emission from multiple fainter sources, we assign
the submillimeter fluxes so that the combined LABOCA plus bright-end ALMA
observed number counts for this field are reproduced. After turning the model
catalogs given by the proxies into submillimeter maps, we perform a source
extraction to include the effects of the observational process on the recovered
counts and galaxy properties. We find that for all proxies, there are lines of
sight giving counts consistent with those derived from LABOCA observations,
even for input sources with randomized positions in the simulated map.
Comparing the recovered redshift, stellar mass and host halo mass distributions
for model SMGs with observational data, we find that the best among the
proposed proxies is that in which the submillimeter luminosity increases
monotonically with the product between dust mass and SFR. This proxy naturally
reproduces a positive trend between SFR and bolometric IR luminosity. The
majority of components of blended sources are spatially unassociated.Comment: 21 pages, 20 figures, 5 tables. Accepted for publication in MNRA
Dark halo baryons not in ancient halo white dwarfs
Having ruled out the possibility that stellar objects are the main
contributor of the dark matter embedding galaxies, microlensing experiments
cannot exclude the hypothesis that a significant fraction of the Milky Way dark
halo might be made of MACHOs with masses in the range 0.5-0.8 \msun. Ancient
white dwarfs are generally considered the most plausible candidates for such
MACHOs. We report the results of a search for such white dwarfs in a proper
motion survey covering a 0.16 sqd field at three epochs at high galactic
latitude, and 0.938 sqd at two epochs at intermediate galactic latitude (VIRMOS
survey), using the CFH telescope. Both surveys are complete to I = 23, with
detection efficiency fading to 0 at I = 24.2. Proper motion data are suitable
to separate unambiguously halo white dwarfs identified by belonging to a non
rotating system. No candidates were found within the colour-magnitude-proper
motion volume where such objects can be safely discriminated from any standard
population as well as from possible artefacts. In the same volume, we estimate
the maximum white dwarf halo fraction compatible with this observation at
different significance levels if the halo is at least 14 gigayears old and
under different ad hoc initial mass functions. Our data alone rules out a halo
fraction greater than 14% at 95% confidence level. Combined with two previous
investigations exploring comparable volumes pushes the limit below 4 % (95%
confidence level) or below 1.3% (64% confidence), this implies that if baryonic
dark matter is present in galaxy halos, it is not, or it is only marginally in
the form of faint hydrogen white dwarfs.Comment: accepted in Astronomy and Astrophysics (19-05-2004
Torque bistability in the interaction between a neutron star magnetosphere and a thin accretion disc
We present a time-dependent model of the interaction between a neutron star
magnetosphere and a thin (Shakura-Sunyaev) accretion disc, where the extent of
the magnetosphere is determined by balancing outward diffusion and inward
advection of the stellar magnetic field at the inner edge of the disc. The
nature of the equilibria available to the system is governed by the magnetic
Prandtl number Pm and the ratio \xi of the corotation radius to the Alfven
radius. For \xi > Pm^0.3, the system can occupy one of two stable states, where
the torques are of opposite signs. If the star is spinning up initially, in the
absence of extraneous perturbations, \xi decreases until the spin-up
equilibrium vanishes, the star subsequently spins down, and the torque
asymptotes to zero. Vortex-in-cell simulations of the Kelvin-Helmholtz
instability suggest that the transport speed across the mixing layer between
the disc and magnetosphere is less than the shear speed when the layer is thin,
unlike in previous models.Comment: 11 pages, 10 figure
Chiral and herringbone symmetry breaking in water-surface monolayers
We report the observation from monolayers of eicosanoic acid in the LâČ2 phase of three distinct out-of-plane first-order diffraction peaks, indicating molecular tilt in a nonsymmetry direction and hence the absence of mirror symmetry. At lower pressures the molecules tilt in the direction of their nearest neighbors. In this region we find a structural transition, which we tentatively identify as the rotator-herringbone transition L2dâL2h
Testing the running of the cosmological constant with Type Ia Supernovae at high z
Within the Quantum Field Theory context the idea of a "cosmological constant"
(CC) evolving with time looks quite natural as it just reflects the change of
the vacuum energy with the typical energy of the universe. In the particular
frame of Ref.[30], a "running CC" at low energies may arise from generic
quantum effects near the Planck scale, M_P, provided there is a smooth
decoupling of all massive particles below M_P. In this work we further develop
the cosmological consequences of a "running CC" by addressing the accelerated
evolution of the universe within that model. The rate of change of the CC stays
slow, without fine-tuning, and is comparable to H^2 M_P^2. It can be described
by a single parameter, \nu, that can be determined from already planned
experiments using SNe Ia at high z. The range of allowed values for \nu follow
mainly from nucleosynthesis restrictions. Present samples of SNe Ia can not yet
distinguish between a "constant" CC or a "running" one. The numerical
simulations presented in this work show that SNAP can probe the predicted
variation of the CC either ruling out this idea or confirming the evolution
hereafter expected.Comment: LaTeX, 51 pages, 13 figures, 1 table, references added, typos
corrected, version accepted in JCA
- âŠ