84,573 research outputs found
Some winter characteristics of the northern high latitude ionosphere
Langmuir probe measurements of ionospheric electron density and temperature during winte
Pass-Through And The Prediction Of Merger Price Effects
We use Monte Carlo experiments to study how pass-through can improve merger price predictions, focusing on the first order approximation (FOA) proposed in Jaffe and Weyl [2013]. FOA addresses the functional form misspecification that can exist in standard merger simulations. We find that the predictions of FOA are tightly distributed around the true price effects if pass-through is precise, but that measurement error in pass-through diminishes accuracy. As a comparison to FOA, we also study a methodology that uses pass-through to select among functional forms for use in simulation. This alternative also increases accuracy relative to standard merger simulation and proves more robust to measurement error
Upward Pricing Pressure As A Predictor Of Merger Price Effects
We use Monte Carlo experiments to evaluate whether “upward pricing pressure” (UPP) accurately predicts the price effects of mergers, motivated by the observation that UPP is a restricted form of the first order approximation derived in Jaffe and Weyl (2013). Results indicate that UPP is quite accurate with standard log-concave demand systems, but understates price effects if demand exhibits greater convexity. Prediction error does not systematically exceed that of misspecified simulation models, nor is it much greater than that of correctly-specified models simulated with imprecise demand elasticities. The results also support that UPP provides accurate screens for anticompetitive mergers
IPLIB (Image processing library) user's manual
IPLIB is a collection of HP FORTRAN 77 subroutines and functions that facilitate the use of a COMTAL image processing system driven by an HP-1000 computer. It is intended for programmers who want to use the HP 1000 to drive the COMTAL Vision One/20 system. It is assumed that the programmer knows HP 1000 FORTRAN 77 or at least one FORTRAN dialect. It is also assumed that the programmer has some familiarity with the COMTAL Vision One/20 system
Grain opacity and the bulk composition of extrasolar planets. I. Results from scaling the ISM opacity
The opacity due to grains in the envelope of a protoplanet regulates the
accretion rate of gas during formation, thus the final bulk composition of
planets with primordial H/He is a function of it. Observationally, for
exoplanets with known mass and radius it is possible to estimate the bulk
composition via internal structure models. We first determine the reduction
factor of the ISM grain opacity f_opa that leads to gas accretion rates
consistent with grain evolution models. We then compare the bulk composition of
synthetic low-mass and giant planets at different f_opa with observations. For
f_opa=1 (full ISM opacity) the synthetic low-mass planets have too small radii,
i.e., too low envelope masses compared to observations. At f_opa=0.003, the
value calibrated with the grain evolution models, synthetic and actual planets
occupy similar mass-radius loci. The mean enrichment of giant planets relative
to the host star as a function of planet mass M can be approximated as
Z_p/Z_star = beta*(M/M_Jup)^alpha. We find alpha=-0.7 independent of f_opa in
synthetic populations in agreement with the observational result (-0.71+-0.10).
The absolute enrichment level decreases from beta=8.5 at f_opa=1 to 3.5 at
f_opa=0. At f_opa=0.003 one finds beta=7.2 which is similar to the
observational result (6.3+-1.0). We thus find observational hints that the
opacity in protoplanetary atmospheres is much smaller than in the ISM even if
the specific value of the grain opacity cannot be constrained here. The result
for the enrichment of giant planets helps to distinguish core accretion and
gravitational instability. In the simplest picture of core accretion where
first a critical core forms and afterwards only gas is added, alpha=-1. If a
core accretes all planetesimals inside the feeding zone, alpha=-2/3. The
observational result lies between these values, pointing to core accretion as
the formation mechanism.Comment: 21 pages, 15 figures. Accepted for A&
Magnetocaloric effect in Gd/W thin film heterostructures
In an effort to understand the impact of nanostructuring on the
magnetocaloric effect, we have grown and studied gadolinium in MgO/W(50
)/[Gd(400 )/W(50 )]
heterostructures. The entropy change associated with the second order magnetic
phase transition was determined from the isothermal magnetization for numerous
temperatures and the appropriate Maxwell relation. The entropy change peaks at
a temperature of 284 K with a value of approximately 3.4 J/kg-K for a 0-30 kOe
field change; the full width at half max of the entropy change peak is about 70
K, which is significantly wider than that of bulk Gd under similar conditions.
The relative cooling power of this nanoscale system is about 240 J/kg, somewhat
lower than that of bulk Gd (410 J/kg). An iterative Kovel-Fisher method was
used to determine the critical exponents governing the phase transition to be
, and . Along with a suppressed Curie temperature
relative to the bulk, the fact that the convergent value of is that
predicted by the 2-D Ising model may suggest that finite size effects play an
important role in this system. Together, these observations suggest that
nanostructuring may be a promising route to tailoring the magnetocaloric
response of materials
A short note on the presence of spurious states in finite basis approximations
The genesis of spurious solutions in finite basis approximations to operators
which possess a continuum and a point spectrum is discussed and a simple
solution for identifying these solutions is suggested
New Challenges For Wind Shock Models: The Chandra Spectrum Of The Hot Star Delta Orionis
The Chandra spectrum of delta Ori A shows emission lines from hydrogen- and helium-like states of Si, Mg, Ne, and O, along with N VII Lyalpha and lines from ions in the range Fe XVII-Fe XXI In contrast to the broad lines seen in zeta Pup and zeta Ori (850 +/- 40 and 1000 +/- 240 km s(-1) half-width at half-maximum [HWHM], respectively), these lines are broadened to only 430 +/- 60 km s(-1) HWHM. This is much lower than the measured wind terminal velocity of 2000 km s(-1). The forbidden, intercombination, and resonance (fir) lines from He-like ions indicate that the majority of the X-ray line emission does not originate at the base of the wind, in agreement with the standard wind shock models for these objects. However, in that model the X-ray emission is distributed throughout an expanding, X-ray-absorbing wind, and it is therefore surprising that the emission lines appear relatively narrow, unshifted, and symmetric. We compare the observed line profiles to recent detailed models for X-ray line pro le generation in hot stars, but none of them offers a fully satisfactory explanation for the observed line profiles
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