308 research outputs found
Ability-Tracking, Instructional Time, and Better Pedagogy: The Effect of Double-Dose Algebra on Student Achievement
This paper provides new evidence on tracking by studying an innovative curriculum implemented by Chicago Public Schools (CPS). In 2003, CPS enacted a double-dose algebra policy requiring 9th grade students with 8th grade math scores below the national median to take two periods of algebra instead of one. This policy led schools to sort students into algebra classes by math ability, so that tracking increased in all algebra classes. We show that double-dosed students are exposed to a much lower-skilled group of peers in their algebra classes but nonetheless benefit substantially from the additional instructional time and improved pedagogy. </jats:p
Mapping Distances Across the Perseus Molecular Cloud Using CO Observations, Stellar Photometry, and Gaia DR2 Parallax Measurements
We present a new technique to determine distances to major star-forming
regions across the Perseus Molecular Cloud, using a combination of stellar
photometry, astrometric data, and spectral-line maps.
Incorporating the Gaia DR2 parallax measurements when available, we start by
inferring the distance and reddening to stars from their Pan-STARRS1 and 2MASS
photometry, based on a technique presented in Green et al. 2014; Green et al.
2015 and implemented in their 3D "Bayestar" dust map of three-quarters of the
sky. We then refine the Green et al. technique by using the velocity slices of
a CO spectral cube as dust templates and modeling the cumulative distribution
of dust along the line of sight towards these stars as a linear combination of
the emission in the slices. Using a nested sampling algorithm, we fit these
per-star distance-reddening measurements to find the distances to the CO
velocity slices towards each star-forming region. This results in distance
estimates explicitly tied to the velocity structure of the molecular gas. We
determine distances to the B5, IC348, B1, NGC1333, L1448, and L1451
star-forming regions and find that individual clouds are located between
pc, with typical combined uncertainties of . We
find that the velocity gradient across Perseus corresponds to a distance
gradient of about 25 pc, with the eastern portion of the cloud farther away
than the western portion. We determine an average distance to the complex of
pc, about 60 pc higher than the distance derived to the western
portion of the cloud using parallax measurements of water masers associated
with young stellar objects. The method we present is not limited to the Perseus
Complex, but may be applied anywhere on the sky with adequate CO data in the
pursuit of more accurate 3D maps of molecular clouds in the solar neighborhood
and beyond.Comment: Accepted for publication in The Astrophysical Journa
Objective course placement and college readiness: evidence from targeted middle school math acceleration
First author draf
Bayesian Methods for Exoplanet Science
Exoplanet research is carried out at the limits of the capabilities of
current telescopes and instruments. The studied signals are weak, and often
embedded in complex systematics from instrumental, telluric, and astrophysical
sources. Combining repeated observations of periodic events, simultaneous
observations with multiple telescopes, different observation techniques, and
existing information from theory and prior research can help to disentangle the
systematics from the planetary signals, and offers synergistic advantages over
analysing observations separately. Bayesian inference provides a
self-consistent statistical framework that addresses both the necessity for
complex systematics models, and the need to combine prior information and
heterogeneous observations. This chapter offers a brief introduction to
Bayesian inference in the context of exoplanet research, with focus on time
series analysis, and finishes with an overview of a set of freely available
programming libraries.Comment: Invited revie
Expanding Economic Opportunity for More Americans: Bipartisan Policies to Increase Work, Wages, and Skills
Many workers today find themselves lacking the skills and training necessary to thrive in the modern economy. Most low- and middle-income workers have not seen meaningful wage increases in many years. Millions of men and women are missing from the workforce altogether. These challenges stem from profound shifts in the American economy and necessitate a dedicated policy response.Over the course of the past year, the Aspen Economic Strategy Group collected policy ideas to address the barriers to broad-based economic opportunity and identified concrete proposals with bipartisan appeal. These proposals are presented here
The Spatial Distribution of Coalescing Neutron Star Binaries: Implications for Gamma-Ray Bursts
We find the distribution of coalescence times, birthrates, spatial
velocities, and subsequent radial offsets of coalescing neutron stars (NSs) in
various galactic potentials accounting for large asymmetric kicks introduced
during a supernovae. The birthrates of bound NS-NS binaries are quite sensitive
to the magnitude of the kick velocities but are, nevertheless, similar (~10 per
Galaxy per Myr) to previous population synthesis studies. The distribution of
merger times since zero-age main sequence is, however, relatively insensitive
to the choice of kick velocities. With a median merger time of ~100 Myr, we
find that compact binaries should closely trace the star formation rate in the
Universe.
In a range of plausible galactic potentials (M_galaxy > 3 x 10^10 M_solar)
the median radial offset of a NS-NS mergers is less than 10 kpc. At a redshift
of z=1 (with H_0 = 65 km/s/Mpc and Omega = 0.2), this means that half the
coalescences should occur within ~1.3 arcsec from the host galaxy. In all but
the most shallow potentials, ninety percent of NS-NS binaries merge within 30
kpc of the host. We find that although the spatial distribution of coalescing
neutron star binaries is consistent with the close spatial association of known
optical afterglows of gamma-ray bursts (GRBs) with faint galaxies, a
non-negligible fraction (~15 percent) of GRBs should occur well outside (>30
kpc) dwarf galaxy hosts. Extinction due to dust in the host, projection of
offsets, and a range in interstellar medium densities confound the true
distribution of NS-NS mergers around galaxies with an observable set of optical
transients/galaxy offsets.Comment: Accepted to MNRAS (12 Jan 1999
The Effects of Doubling Instruction Efforts on Middle School Students' Achievement: Evidence from a Multiyear Regression-Discontinuity Design
- …