896 research outputs found
Assessing the causal effects of a stochastic intervention in time series data: Are heat alerts effective in preventing deaths and hospitalizations?
We introduce a new causal inference framework for time series data aimed at
assessing the effectiveness of heat alerts in reducing mortality and
hospitalization risks. We are interested in addressing the following question:
how many deaths and hospitalizations could be averted if we were to increase
the frequency of issuing heat alerts in a given location? In the context of
time series data, the overlap assumption - each unit must have a positive
probability of receiving the treatment - is often violated. This is because, in
a given location, issuing a heat alert is a rare event on an average
temperature day as heat alerts are almost always issued on extremely hot days.
To overcome this challenge, first we introduce a new class of causal estimands
under a stochastic intervention (i.e., increasing the odds of issuing a heat
alert) for a single time series corresponding to a given location. We develop
the theory to show that these causal estimands can be identified and estimated
under a weaker version of the overlap assumption. Second, we propose
nonparametric estimators based on time-varying propensity scores, and derive
point-wise confidence bands for these estimators. Third, we extend this
framework to multiple time series corresponding to multiple locations. Via
simulations, we show that the proposed estimator has good performance with
respect to bias and root mean squared error. We apply our proposed method to
estimate the causal effects of increasing the odds of issuing heat alerts in
reducing deaths and hospitalizations among Medicare enrollees in 2817 U.S.
counties. We found weak evidence of a causal link between increasing the odds
of issuing heat alerts during the warm seasons of 2006-2016 and a reduction in
deaths and cause-specific hospitalizations across the 2817 counties.Comment: 31 pages, 5 figures, 2 table
Non-Gaussian Correlations in the McLerran-Venugopalan Model
We argue that the statistical weight function W[rho] appearing in the
McLerran-Venugopalan model of a large nucleus is intrinsically non-Gaussian,
even if we neglect quantum corrections. Based on the picture where the nucleus
of radius R consists of a collection of color-neutral nucleons, each of radius
a<<R, we show that to leading order in alpha_s and a/R only the Gaussian part
of W[rho] enters into the final expression for the gluon number density. Thus,
the existing results in the literature which assume a Gaussian weight remain
valid.Comment: 21 pages with 4 figures (revtex
Form factor for a family of quantum graphs: An expansion to third order
For certain types of quantum graphs we show that the random-matrix form
factor can be recovered to at least third order in the scaled time from
periodic-orbit theory. We consider the contributions from pairs of periodic
orbits represented by diagrams with up to two self-intersections connected by
up to four arcs and explain why all other diagrams are expected to give
higher-order corrections only.
For a large family of graphs with ergodic classical dynamics the diagrams
that exist in the absence of time-reversal symmetry sum to zero. The mechanism
for this cancellation is rather general which suggests that it may also apply
at higher-orders in the expansion. This expectation is in full agreement with
the fact that in this case the linear- contribution, the diagonal
approximation, already reproduces the random-matrix form factor for .
For systems with time-reversal symmetry there are more diagrams which
contribute at third order. We sum these contributions for quantum graphs with
uniformly hyperbolic dynamics, obtaining , in agreement with
random-matrix theory. As in the previous calculation of the leading-order
correction to the diagonal approximation we find that the third order
contribution can be attributed to exceptional orbits representing the
intersection of diagram classes.Comment: 23 pages (including 4 fig.) - numerous typos correcte
The NASA-UC-UH Eta-Earth Program: IV. A Low-mass Planet Orbiting an M Dwarf 3.6 PC from Earth
We report the discovery of a low-mass planet orbiting Gl 15 A based on radial
velocities from the Eta-Earth Survey using HIRES at Keck Observatory. Gl 15 Ab
is a planet with minimum mass Msini = 5.35 0.75 M, orbital
period P = 11.4433 0.0016 days, and an orbit that is consistent with
circular. We characterize the host star using a variety of techniques.
Photometric observations at Fairborn Observatory show no evidence for
rotational modulation of spots at the orbital period to a limit of ~0.1 mmag,
thus supporting the existence of the planet. We detect a second RV signal with
a period of 44 days that we attribute to rotational modulation of stellar
surface features, as confirmed by optical photometry and the Ca II H & K
activity indicator. Using infrared spectroscopy from Palomar-TripleSpec, we
measure an M2 V spectral type and a sub-solar metallicity ([M/H] = -0.22,
[Fe/H] = -0.32). We measure a stellar radius of 0.3863 0.0021 R
based on interferometry from CHARA.Comment: ApJ accepted, 11 pages, 8 figures, 3 table
On Superspace Chern-Simons-like Terms
We search for superspace Chern-Simons-like higher-derivative terms in the low
energy effective actions of supersymmetric theories in four dimensions.
Superspace Chern-Simons-like terms are those gauge-invariant terms which cannot
be written solely in terms of field strength superfields and covariant
derivatives, but in which a gauge potential superfield appears explicitly. We
find one class of such four-derivative terms with N=2 supersymmetry which,
though locally on the Coulomb branch can be written solely in terms of field
strengths, globally cannot be. These terms are classified by certain Dolbeault
cohomology classes on the moduli space. We include a discussion of other
examples of terms in the effective action involving global obstructions on the
Coulomb branch.Comment: 23 pages; a reference and an author email correcte
Touchstone Stars: Highlights from the Cool Stars 18 Splinter Session
We present a summary of the splinter session on "touchstone stars" -- stars
with directly measured parameters -- that was organized as part of the Cool
Stars 18 conference. We discuss several methods to precisely determine cool
star properties such as masses and radii from eclipsing binaries, and radii and
effective temperatures from interferometry. We highlight recent results in
identifying and measuring parameters for touchstone stars, and ongoing efforts
to use touchstone stars to determine parameters for other stars. We conclude by
comparing the results of touchstone stars with cool star models, noting some
unusual patterns in the differences.Comment: Proceedings of the 18th Cambridge Workshop on Cool Stars, Stellar
Systems, and the Sun, Eds G. van Belle & H. Harri
Improved Orbital Parameters and Transit Monitoring for HD 156846b
HD 156846b is a Jovian planet in a highly eccentric orbit (e = 0.85) with a
period of 359.55 days. The pericenter passage at a distance of 0.16 AU is
nearly aligned to our line of sight, offering an enhanced transit probability
of 5.4% and a potentially rich probe of the dynamics of a cool planetary
atmosphere impulsively heated during close approach to a bright star (V = 6.5).
We present new radial velocity (RV) and photometric measurements of this star
as part of the Transit Ephemeris Refinement and Monitoring Survey (TERMS). The
RV measurements from Keck-HIRES reduce the predicted transit time uncertainty
to 20 minutes, an order of magnitude improvement over the ephemeris from the
discovery paper. We photometrically monitored a predicted transit window under
relatively poor photometric conditions, from which our non-detection does not
rule out a transiting geometry. We also present photometry that demonstrates
stability at the millimag level over its rotational timescale.Comment: 7 pages, 4 figures, accepted for publication in Ap
The HD 192263 system: planetary orbital period and stellar variability disentangled
As part of the Transit Ephemeris Refinement and Monitoring Survey (TERMS), we
present new radial velocities and photometry of the HD 192263 system. Our
analysis of the already available Keck-HIRES and CORALIE radial velocity
measurements together with the five new Keck measurements we report in this
paper results in improved orbital parameters for the system. We derive
constraints on the size and phase location of the transit window for HD
192263b, a Jupiter-mass planet with a period of 24.3587 \pm 0.0022 days. We use
10 years of Automated Photoelectric Telescope (APT) photometry to analyze the
stellar variability and search for planetary transits. We find continuing
evidence of spot activity with periods near 23.4 days. The shape of the
corresponding photometric variations changes over time, giving rise to not one
but several Fourier peaks near this value. However, none of these frequencies
coincides with the planet's orbital period and thus we find no evidence of
star-planet interactions in the system. We attribute the ~23-day variability to
stellar rotation. There are also indications of spot variations on longer (8
years) timescales. Finally, we use the photometric data to exclude transits for
a planet with the predicted radius of 1.09 RJ, and as small as 0.79 RJ.Comment: 9 pages, 6 tables, 6 figures; accepted to Ap
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