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  1. Free, publicly-accessible full text available April 1, 2023
  2. Abstract We present 870 μ m Atacama Large Millimeter/submillimeter Array polarization observations of thermal dust emission from the iconic, edge-on debris disk β Pic. While the spatially resolved map does not exhibit detectable polarized dust emission, we detect polarization at the ∼3 σ level when averaging the emission across the entire disk. The corresponding polarization fraction is P frac = 0.51% ± 0.19%. The polarization position angle χ is aligned with the minor axis of the disk, as expected from models of dust grains aligned via radiative alignment torques (RAT) with respect to a toroidal magnetic field ( B -RAT)more »or with respect to the anisotropy in the radiation field ( k -RAT). When averaging the polarized emission across the outer versus inner thirds of the disk, we find that the polarization arises primarily from the SW third. We perform synthetic observations assuming grain alignment via both k -RAT and B -RAT. Both models produce polarization fractions close to our observed value when the emission is averaged across the entire disk. When we average the models in the inner versus outer thirds of the disk, we find that k -RAT is the likely mechanism producing the polarized emission in β Pic. A comparison of timescales relevant to grain alignment also yields the same conclusion. For dust grains with realistic aspect ratios (i.e., s > 1.1), our models imply low grain-alignment efficiencies.« less
    Free, publicly-accessible full text available May 1, 2023
  3. Cu3Sn, a well-known intermetallic compound with a high melting temperature and thermal stability, has found numerous applications in microelectronics, 3D printing, and catalysis. However, the relationship between the material's thermal conductivity anisotropy and its complex anti-phase boundary superstructure is not well understood. Here, frequency domain thermoreflectance was used to map the thermal conductivity variation across the surface of arc-melted polycrystalline Cu3Sn. Complementary electron backscatter diffraction and transmission electron microscopy revealed the thermal conductivity in the principal a, b, and c orientations to be 57.6, 58.9, and 67.2 W/m-K, respectively. Density functional theory calculations for several Cu3Sn superstructures helped examine thermodynamicmore »stability factors and evaluate the direction-resolved electron transport properties in the relaxation time approximation. The analysis of computed temperature- and composition-dependent free energies suggests metastability of the known long-period Cu3Sn superstructures while the transport calculations indicate a small directional variation in the thermal conductivity. The ∼15% anisotropy measured and computed in this study is well below previously reported experimental values for samples grown by liquid-phase electroepitaxy.« less
    Free, publicly-accessible full text available April 1, 2023
  4. Abstract One of the primary goals for the upcoming James Webb Space Telescope is to observe the first galaxies. Predictions for planned and proposed surveys have typically focused on average galaxy counts, assuming a random distribution of galaxies across the observed field. The first and most-massive galaxies, however, are expected to be tightly clustered, an effect known as cosmic variance. We show that cosmic variance is likely to be the dominant contribution to uncertainty for high-redshift mass and luminosity functions, and that median high-redshift and high-mass galaxy counts for planned observations lie significantly below average counts. Several different strategies aremore »considered for improving our understanding of the first galaxies, including adding depth, area, and independent pointings. Adding independent pointings is shown to be the most efficient both for discovering the single highest-redshift galaxy and also for constraining mass and luminosity functions.« less
    Free, publicly-accessible full text available December 1, 2022
  5. Free, publicly-accessible full text available January 1, 2023
  6. Free, publicly-accessible full text available March 1, 2023
  7. Abstract One of the basic goals of second language (L2) speech research is to understand the perception-production link, or the relationship between L2 speech perception and L2 speech production. Although many studies have examined the link, they have done so with strikingly different conceptual foci and methods. Even studies that appear to use similar perception and production tasks often present nontrivial differences in task characteristics and implementation. This conceptual and methodological variation makes meaningful synthesis of perception-production findings difficult, and it also complicates the process of developing new perception-production models that specifically address how the link changes throughout L2 learning.more »In this study, we scrutinize theoretical and methodological issues in perception-production research and offer recommendations for advancing theory and practice in this domain. We focus on L2 sound learning because most work in the area has focused on segmental contrasts.« less