Sorting and inequality in Canadian schools

Researchers and educators often argue that a student's peers strongly influence his or her educational outcomes. If so, an unequal distribution of advantaged and disadvantaged students across schools in a community will leave many students doubly disadvantaged and amplify existing inequalities. We explore the relationship between the degree of sorting by socioeconomic characteristics, ethnicity and language across schools within a community and inequality as measured by the variance of standardized high school exam scores within the community. Simple cross- sectional estimates suggest a direct relationship between sorting by ethnicity and the variance of test scores, but no direct relationship between sorting by income or primary parent's education and the variance of test scores. We then implement a fixed effects estimator to control for endogeneity in the extent of sorting: the results indicate that sorting by ethnicity does not affect the variance of test scores, but that sorting by home language and primary parent's education does.social interactions, peer effects, sorting, classroom effects

Sorting, Peers and Achievement of Aboriginal Students in British Columbia

We use administrative data on students in grades 4 and 7 in British Columbia to examine the extent to which differences in school environment contribute to the achievement gap between Aboriginal and non-Aboriginal students as measured by standardized test scores. We find that segregation of Aboriginal and non-Aboriginal students is substantial, and that differences in the distribution of these two groups across schools account for roughly half the overall achievement gap on the Foundation Skills Assessment tests in grade 7. The substantial school-level segregation of Aboriginal and non-Aboriginal student across schools means that Aboriginal students on average have a higher proportion of peers who are themselves Aboriginal, as well as a higher proportion of peers in special education. We estimate the effect of peer composition on value-added exam outcomes, using longitudinal data on multiple cohorts of students together with school-by-grade fixed effects to account for endogenous selection into schools. We find that having a greater proportion of Aboriginal peers, if anything, improves the achievement of Aboriginal students.Aboriginal education, peer effects

Spectrum Formation at Late Times in Type Ia Supernovae

I present a study of radiative transfer effects in type Ia supernovae ranging from 3-4 months to nearly 2 years post-maximum light. I explore several components of spectrum formation, beginning with a semi-analytic model which examines the behavior of line scattering in an optically thin medium, reminiscent of SN Ia ejecta at late times, and compare such behavior with the effects of line scattering at early times in SNe Ia, when the ejecta are optically thick. The model shows that line scattering produces spectral features similar to P Cygni profiles found near maximum light in SNe, but with subtle wavelength shifts which may lead to misidentified lines in observed spectra if these effects are not taken into account. Next, I present near-infrared synthetic spectra from numerical calculations with the general-purpose radiative transfer code PHOENIX, and compare them to observations obtained of four normal type Ia supernovae several months post-maximum light, including the recent and nearby SN 2014J. Such comparisons reveal that, even this late in a supernova’s life, permitted lines of iron-peak elements comprise most of the near-infrared spectrum. In addition, an emission feature from [Ni II] near 2 μm indicates that electron capture during high-density nuclear burning likely takes place in a significant fraction of type Ia supernovae. Such high-density burning is difficult to obtain in explosions of sub-Chandrasekhar-mass progenitors, e.g., white dwarf mergers. Finally I perform spectrum calculations at even later epochs, from 100 to 578 days after maximum light, and compare the results to the observed optical and ultraviolet spectra of the nearby SN 2011fe. I find that, contrary to much of the literature, our models fit SN 2011fe at day +100 without accounting for any forbidden atomic lines; the optical spectrum consists primarily of permitted Fe II and Ca II. Including forbidden lines and repeating the same calculation yields similar optical spectra, but with quite different atomic lines contributing to most of the features, leading to a curious degeneracy among interpretations of spectra at this epoch. At later epochs, forbidden emission from Fe II and Fe III form most of the optical spectrum, although the H & K doublet of Ca II continues to play a role in the emission near 4000 A. In the ultraviolet spectrum at day +360, the SED is optically thick, and most of the spectrum consists of permitted lines of various iron-peak species. These results show that the transition to the “nebular” phase in type Ia supernovae is more complicated than frequently assumed in the literature, and is highly wavelength-dependent

Supernova Resonance--scattering Line Profiles in the Absence of a Photosphere

In supernova spectroscopy relatively little attention has been given to the properties of optically thick spectral lines in epochs following the photosphere's recession. Most treatments and analyses of post-photospheric optical spectra of supernovae assume that forbidden-line emission comprises most if not all spectral features. However, evidence exists which suggests that some spectra exhibit line profiles formed via optically thick resonance-scattering even months or years after the supernova explosion. To explore this possibility we present a geometrical approach to supernova spectrum formation based on the "Elementary Supernova" model, wherein we investigate the characteristics of resonance-scattering in optically thick lines while replacing the photosphere with a transparent central core emitting non-blackbody continuum radiation, akin to the optical continuum provided by decaying 56Co formed during the explosion. We develop the mathematical framework necessary for solving the radiative transfer equation under these conditions, and calculate spectra for both isolated and blended lines. Our comparisons with analogous results from the Elementary Supernova code SYNOW reveal several marked differences in line formation. Most notably, resonance lines in these conditions form P Cygni-like profiles, but the emission peaks and absorption troughs shift redward and blueward, respectively, from the line's rest wavelength by a significant amount, despite the spherically symmetric distribution of the line optical depth in the ejecta. These properties and others that we find in this work could lead to misidentification of lines or misattribution of properties of line-forming material at post-photospheric times in supernova optical spectra.Comment: 37 pages, 24 figures; accepted for publication in ApJ Supplement Serie

Of Tools and Houses: Sociologists Without Borders and the AAAS Science and Human Rights Coalition

Sociologists Without Borders (SSF) has played a key role in the Science and Human Rights Coalition (SHRC) of the American Association for the Advancement of Science. This Coalition, which consists of nearly fifty scientific organizations, seeks to advance the human right to benefit from scientific progress and its application. This article critically evaluates SSF’s role in the SHRC. After providing background on the work, organization, and objectives of the Coalition, this article then elaborates on how sociologists, particularly representatives of the American Sociological Association and SSF, have collaborated with other scientists on various projects designed to implement this human right. These collaborative efforts give reason for hope. They suggest that science is being used to work towards greater equality and justice, and that SSF plays a positive role in this effort through its alliance with the SHR

Galactos: Computing the Anisotropic 3-Point Correlation Function for 2 Billion Galaxies

The nature of dark energy and the complete theory of gravity are two central questions currently facing cosmology. A vital tool for addressing them is the 3-point correlation function (3PCF), which probes deviations from a spatially random distribution of galaxies. However, the 3PCF's formidable computational expense has prevented its application to astronomical surveys comprising millions to billions of galaxies. We present Galactos, a high-performance implementation of a novel, O(N^2) algorithm that uses a load-balanced k-d tree and spherical harmonic expansions to compute the anisotropic 3PCF. Our implementation is optimized for the Intel Xeon Phi architecture, exploiting SIMD parallelism, instruction and thread concurrency, and significant L1 and L2 cache reuse, reaching 39% of peak performance on a single node. Galactos scales to the full Cori system, achieving 9.8PF (peak) and 5.06PF (sustained) across 9636 nodes, making the 3PCF easily computable for all galaxies in the observable universe.Comment: 11 pages, 7 figures, accepted to SuperComputing 201

Microbial Communities Associated With Stable Fly (Diptera: Muscidae) Larvae and Their Developmental Substrates

Bacteria are essential for stable fly (Stomoxys calcitrans (L.)) larval survival and development, but little is known about the innate microbial communities of stable flies, and it is not known if their varied dietary substrates influence their gut microbial communities. This investigation utilized 454 sequencing of 16S and 18S amplicons to characterize and compare the bacterial and eukaryotic microbial communities in stable fly larvae and their developmental substrates. The microbial community of the third-instar stable fly larvae is unambiguously distinct from the microbial community of the supporting substrate, with bacterial communities from larvae reared on different substrates more similar to each other than to the communities from their individual supporting substrates. Bacterial genera that were more abundant proportionally in larvae compared to their substrates were Erysipelothrix, Dysgonomonas, Ignatzschineria (Gammaproteobacteria), and Campylobacter (Epsilonprotobacteria). The alphaproteobacteria Devosia, Brevundimonas, Sphingopyxix, and Paracoccus were more abundant proportionally in field substrates compared to their larvae. The main genera responsible for differences between the positive and negative field substrates were Dysgonomonas and Proteiniphilum. In contrast to Dysgonomonas, Proteiniphilum was more abundant in substrate than in the larvae. A large number of sequences were assigned to an unclassified protest of the superphylum Alveolata in larvae and their substrate. Microscopy validated these findings and a previously undescribed gregarine (phylum Apicomplexa, class Conoidasida) was identified in stable fly larvae and adults

Near-infrared line identification in type Ia supernovae during the transitional phase

We present near-infrared synthetic spectra of a delayed-detonation hydrodynamical model and compare them to observed spectra of four normal type Ia supernovae ranging from day +56.5 to day +85. This is the epoch during which supernovae are believed to be undergoing the transition from the photospheric phase, where spectra are characterized by line scattering above an optically thick photosphere, to the nebular phase, where spectra consist of optically thin emission from forbidden lines. We find that most spectral features in the near-infrared can be accounted for by permitted lines of Fe II and Co II. In addition, we find that [Ni II] fits the emission feature near 1.98 {\mu}m, suggesting that a substantial mass of 58Ni exists near the center of the ejecta in these objects, arising from nuclear burning at high density. A tentative identification of Mn II at 1.15 {\mu}m may support this conclusion as well.Comment: accepted to Ap