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1. New Astrometric Measurements of the Position Angle and Separation of the Double Star System WDS 03245+5938 STI 450

   Marcel, M C; Sani, I A; JGerald, J L; Pius, P; Ekwu, O M; Bvumbwe, B; Sudum, E; Olayiwola, J U (January 2024, Journal of Double Star Observations)

   Freed, R; Harshaw, R; Genet, Russell M (Ed.)

   We report new measurements of the position angle and separation of the double star WDS 03245+5938 STI 450, based on our observations, Gaia EDR3, and historical data. We find that the position angle and separation are 209.7° and 7.68", respectively, showing slight changes from the previous values of 210° and 7.742". We also find that the distances between the two stars are far apart, suggesting that the system is an optical double, and therefore not gravitationally bound together. Furthermore, we find that the ratio of proper motion (rPM) metric of the system is distinct, indicating that the system is a chance alignment of two unrelated stars that are at different distances. 

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2. Inelastic neutron scattering evidence for anomalous H–H distances in metal hydrides

   https://doi.org/10.1073/pnas.1912900117  

   Borgschulte, Andreas; Terreni, Jasmin; Billeter, Emanuel; Daemen, Luke; Cheng, Yongqiang; Pandey, Anup; Łodziana, Zbigniew; Hemley, Russell J.; Ramirez-Cuesta, Anibal J. (February 2020, Proceedings of the National Academy of Sciences)

   Hydrogen-containing materials are of fundamental as well as technological interest. An outstanding question for both is the amount of hydrogen that can be incorporated in such materials, because that determines dramatically their physical properties such as electronic and crystalline structure. The number of hydrogen atoms in a metal is controlled by the interaction of hydrogens with the metal and by the hydrogen–hydrogen interactions. It is well established that the minimal possible hydrogen–hydrogen distances in conventional metal hydrides are around 2.1 Å under ambient conditions, although closer H–H distances are possible for materials under high pressure. We present inelastic neutron scattering measurements on hydrogen in Z r V 2 H x showing nonexpected scattering at low-energy transfer. The analysis of the spectra reveals that these spectral features in part originate from hydrogen vibrations confined by neighboring hydrogen at distances as short as 1.6 Å. These distances are much smaller than those found in related hydrides, thereby violating the so-called Switendick criterion. The results have implications for the design and creation of hydrides with additional properties and applications. 

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3. Which Distribution Distances are Sublinearly Testable?

   Daskalakis, Constantinos; Kamath, Gautam; Wright, John (January 2018, Proceedings of the annual ACM-SIAM Symposium on Discrete Algorithms)

   Given samples from an unknown distribution p and a description of a distribution q, are p and q close or far? This question of “identity testing” has received significant attention in the case of testing whether p and q are equal or far in total variation distance. However, in recent work [VV11a, ADK15, DP17], the following questions have been been critical to solving problems at the frontiers of distribution testing: Alternative Distances: Can we test whether p and q are far in other distances, say Hellinger? Tolerance: Can we test when p and q are close, rather than equal? And if so, close in which distances? Motivated by these questions, we characterize the complexity of distribution testing under a variety of distances, including total variation, ℓ2, Hellinger, Kullback-Leibler, and χ2. For each pair of distances d1 and d2, we study the complexity of testing if p and q are close in d1 versus far in d2, with a focus on identifying which problems allow strongly sublinear testers (i.e., those with complexity O(n1–γ) for some γ > 0 where n is the size of the support of the distributions p and q). We provide matching upper and lower bounds for each case. We also study these questions in the case where we only have samples from q (equivalence testing), showing qualitative differences from identity testing in terms of when tolerance can be achieved. Our algorithms fall into the classical paradigm of χ2-statistics, but require crucial changes to handle the challenges introduced by each distance we consider. Finally, we survey other recent results in an attempt to serve as a reference for the complexity of various distribution testing problems. 

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4. Better Distance Preservers and Additive Spanners

   https://doi.org/10.1145/3490147  

   Bodwin, Greg; Williams, Virginia Vassilevska (October 2021, ACM Transactions on Algorithms)

   We study two popular ways to sketch the shortest path distances of an input graph. The first is distance preservers , which are sparse subgraphs that agree with the distances of the original graph on a given set of demand pairs. Prior work on distance preservers has exploited only a simple structural property of shortest paths, called consistency , stating that one can break shortest path ties such that no two paths intersect, split apart, and then intersect again later. We prove that consistency alone is not enough to understand distance preservers, by showing both a lower bound on the power of consistency and a new general upper bound that polynomially surpasses it. Specifically, our new upper bound is that any p demand pairs in an n -node undirected unweighted graph have a distance preserver on O( n 2/3 p 2/3 + np 1/3 edges. We leave a conjecture that the right bound is O ( n 2/3 p 2/3 + n ) or better. The second part of this paper leverages these distance preservers in a new construction of additive spanners , which are subgraphs that preserve all pairwise distances up to an additive error function. We give improved error bounds for spanners with relatively few edges; for example, we prove that all graphs have spanners on O(n) edges with + O ( n 3/7 + ε ) error. Our construction can be viewed as an extension of the popular path-buying framework to clusters of larger radii. 

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5. Stellar Metallicities from DECam u-band Photometry: A Study of Milky Way Ultra-faint Dwarf Galaxies

   https://doi.org/10.3847/1538-4357/ad9820  

   Pan, Yue; Chiti, Anirudh; Drlica-Wagner, Alex; Ji, Alexander P; Li, Ting S; Limberg, Guilherme; Tucker, Douglas L; Allam, Sahar (December 2024, The Astrophysical Journal)

   Abstract We conducted an in-depth analysis of candidate member stars located in the peripheries of three ultra-faint dwarf (UFD) galaxy satellites of the Milky Way (MW): Boötes I (Boo1), Boötes II (Boo2), and Segue I (Seg1). Studying these peripheral stars has previously been difficult due to contamination from the MW foreground. We usedu-band photometry from the Dark Energy Camera (DECam) to derive metallicities to efficiently select UFD candidate member stars. This approach was validated on Boo1, where we identified both previously known and new candidate member stars beyond five half-light radii. We then applied a similar procedure to Boo2 and Seg1. Our findings hinted at evidence for tidal features in Boo1 and Seg1, with Boo1 having an elongation consistent with its proper motion and Seg1 showing some distant candidate stars, a few of which are along its elongation and proper motion. We find two Boo2 stars at large distances consistent with being candidate member stars. Using a foreground contamination rate derived from the Besançon Galaxy model, we ascribed purity estimates to each candidate member star. We recommend further spectroscopic studies on the newly identified high-purity members. Our technique offers promise for future endeavors to detect candidate member stars at large radii in other systems, leveraging metallicity-sensitive filters with the Legacy Survey of Space and Time and the new, narrowband Ca HK filter on DECam. 

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