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U.S. Immigration Policies Pose a Threat to the Human Rights of Guatemalan, Salvadoran, and Mexican Immigrant Women
No full textModeling optical roughness and first-order scattering processes from OSIRIS-REx color images of the rough surface of asteroid (101955) Bennu
No full text© 2020 Elsevier Inc. The dark asteroid (101955) Bennu studied by NASA’ s OSIRIS-REx mission has a boulder-rich and apparently dust-poor surface, providing a natural laboratory to investigate the role of single-scattering processes in rough particulate media. Our goal is to define optical roughness and other scattering parameters that may be useful for the laboratory preparation of sample analogs, interpretation of imaging data, and analysis of the sample that will be returned to Earth. We rely on a semi-numerical statistical model aided by digital terrain model (DTM) shadow ray-tracing to obtain scattering parameters at the smallest surface element allowed by the DTM (facets of ~10 cm). Using a Markov Chain Monte Carlo technique, we solved the inversion problem on all four-band images of the OSIRIS-REx mission’ s top four candidate sample sites, for which high-precision laser altimetry DTMs are available. We reconstructed the a posteriori probability distribution for each parameter and distinguished primary and secondary solutions. Through the photometric image correction, we found that a mixing of low and average roughness slope best describes Bennu\u27s surface for up to 90∘ phase angle. We detected a low non-zero specular ratio, perhaps indicating exposed sub-centimeter mono-crystalline inclusions on the surface. We report an average roughness RMS slope of 27−5∘+1, a specular ratio of 2.6−0.8+0.1%, an approx. single-scattering albedo of 4.64−0.09+0.08% at 550 nm, and two solutions for the back-scatter asymmetric factor, ξ(1) = − 0.360 ± 0.030 and ξ(2) = − 0.444 ± 0.020, for all four sites altogether
Better 3-coloring algorithms: Excluding a triangle and a seven vertex path
No full text© 2020 Elsevier B.V. We present an algorithm to color a graph G with no triangle and no induced 7-vertex path (i.e., a {P7,C3}-free graph), where every vertex is assigned a list of possible colors which is a subset of {1,2,3}. While this is a special case of the problem solved in Bonomo et al. (2018) [1], that does not require the absence of triangles, the algorithm here is both faster and conceptually simpler. The complexity of the algorithm is O(|V(G)|5(|V(G)|+|E(G)|)), and if G is bipartite, it improves to O(|V(G)|2(|V(G)|+|E(G)|)). Moreover, we prove that there are finitely many minimal obstructions to list 3-coloring {Pt,C3}-free graphs if and only if t≤7. This implies the existence of a polynomial time certifying algorithm for list 3-coloring in {P7,C3}-free graphs. We furthermore determine other cases of t,ℓ, and k such that the family of minimal obstructions to list k-coloring in {Pt,Cℓ}-free graphs is finite
