This chapter summarizes the findings of 32 years of research from all of our longitudinal studies to date, conducted in 36 school districts in 16 U.S. states, more than 7.5 million student records analyzed, following English learners (of all language backgrounds) as far as Grades K–12. These studies are very generalizable to all regions and contexts of the United States and have been replicated in other countries, answering questions regarding program effectiveness for policymakers in education. We have shown that English-only and transitional bilingual programs of short duration only close about half of the achievement gap between English learners and native English speakers, while high-quality, long-term bilingual programs close all of the gap after 5–6 years of schooling through the students’ first and second languages (L1 and L2). In addition, our studies answer the linguistic question of how long it takes student groups to reach grade-level achievement in their L2, and we have developed and refined our theoretical Prism model by collecting and analyzing program effectiveness data, basing the Prism model on our empirical findings.
Context. We present results from the first recorded stellar occultation by the large trans-Neptunian object (174567) Varda that was observed on September 10, 2018. Varda belongs to the high-inclination dynamically excited population, and has a satellite, Ilmarë, which is half the size of Varda.
Aims. We determine the size and albedo of Varda and constrain its 3D shape and density.
Methods. Thirteen different sites in the USA monitored the event, five of which detected an occultation by the main body. A best-fitting ellipse to the occultation chords provides the instantaneous limb of the body, from which the geometric albedo is computed. The size and shape of Varda are evaluated, and its bulk density is constrained using Varda’s mass as is known from previous works.
Results. The best-fitting elliptical limb has semi-major (equatorial) axis of (383 ± 3) km and an apparent oblateness of 0.066 ± 0.047, corresponding to an apparent area-equivalent radius R′equiv = (370±7) km and geometric albedo pv = 0.099 ± 0.002 assuming a visual absolute magnitude HV = 3.81 ± 0.01. Using three possible rotational periods for the body (4.76, 5.91, and 7.87 h), we derive corresponding MacLaurin solutions. Furthermore, given the low-amplitude (0.06 ± 0.01) mag of the single-peaked rotational light-curve for the aforementioned periods, we consider the double periods. For the 5.91 h period (the most probable) and its double (11.82 h), we find bulk densities and true oblateness of ρ = (1.78 ± 0.06) g cm−3, ɛ = 0.235 ± 0.050, and ρ = (1.23 ± 0.04) g cm−3, ɛ = 0.080 ± 0.049. However, it must be noted that the other solutions cannot be excluded just yet.
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