Search for: All records

The tip of the red giant branch (TRGB) provides a luminous standard candle for constructing distance ladders to measure the Hubble constant. In practice, its measurements via edge-detection response (EDR) are complicated by the apparent fuzziness of the tip and the multipeak landscape of the EDR. Previously, we optimized an unsupervised algorithm, Comparative Analysis of TRGBs, to minimize the variance among multiple halo fields per host without relying on individualized choices, achieving state-of-the-art ∼<0.05 mag distance measures for optimal data. Here we apply this algorithm to an expanded sample of SN Ia hosts to standardize these to multiple fields in the geometric anchor, NGC 4258. In concert with the Pantheon+ SN Ia sample, this analysis produces a (baseline) result ofH₀= 73.22 ± 2.06 km s⁻¹Mpc⁻¹. The largest difference inH₀between this and similar studies employing the TRGB derives from corrections for SN survey differences and local flows used in the most recent SN Ia compilations that were absent in earlier studies. The SN-related differences total ∼2.0 km s⁻¹Mpc⁻¹. A smaller share, ∼1.4 km s⁻¹Mpc⁻¹, results from the inhomogeneity of the TRGB calibration across the distance ladder. We employ a grid of 108 variants around the optimal TRGB algorithm and find that the median of the variants is 72.94 ± 1.98 km s⁻¹Mpc⁻¹with an additional uncertainty due to algorithm choices of 0.83 km s⁻¹Mpc⁻¹. None of these TRGB variants result in anH₀of less than 71.6 km s⁻¹Mpc⁻¹.

 

This research paper describes a study designed to help inform STEM faculty hiring practices at institutions of higher education in the U.S., where over the past two decades, diversity statements have become more popular components of application packages for faculty jobs. The purpose is to explore the ways and extent to which diversity statements are utilized in evaluating faculty applicants. The research questions are: (1) To what extent do universities equip search committees to evaluate applicants’ diversity statements? (2) What are STEM faculty’s perspectives of diversity statements in job applications? This paper is derived from a larger two-phase sequential mixed methods study examining the factors current faculty members and administrators consider important when hiring new STEM faculty. During the first phase, we deployed a nationwide survey to STEM faculty members and administrators who have been involved in faculty searches, with 151 of 216 respondents answering questions specific to diversity statements. About 29% of survey respondents indicated their departments required diversity statements; 59% indicated their institutions did not provide guidance for evaluating them. The second phase was a phenomenological study involving interviews of 25 survey respondents. Preliminary analyses of interview data indicated that a little more than half (52%) of participants’ departments required a diversity statement. Of the departments that required diversity statements, a little more than half used a rubric for evaluation, whether as part of a larger holistic rubric, or as a standalone rubric. For some departments that did not require diversity statements, applicants were required to discuss diversity within their other application materials. Regarding faculty members’ perceptions of diversity statements, some felt that diversity statements were necessary to assess candidates’ beliefs and experiences. Some noted that when diversity is discussed as part of another document and is not required as a stand-alone statement, it feels like the candidate “slaps on a paragraph” about diversity. Others viewed diversity statements as a “bump” that gives candidates “bonus points.” A few faculty felt that diversity statements were “redundant,” and if applicants were passionate about diversity, they would organically discuss it in the other required documents. Many shared frustrations regarding the requirement and evaluation practices. Most participants indicated their postings provided applicants with little to no guidance on what search committees were looking for in submitted diversity statements; they felt it would be beneficial for both the search committee and the applicants to have this guidance. Shared through a traditional lecture, results from this study may be used to help inform strategies for recruiting faculty who are committed to diversity - and ideally, equity and inclusion - and for addressing equity in faculty hiring. 

Abstract 

The current and next observation seasons will detect hundreds of gravitational waves (GWs) from compact binary systems coalescence at cosmological distances. When combined with independent electromagnetic measurements, the source redshift will be known, and we will be able to obtain precise measurements of the Hubble constant H0 via the distance–redshift relation. However, most observed mergers are not expected to have electromagnetic counterparts, which prevents a direct redshift measurement. In this scenario, one possibility is to use the dark sirens method that statistically marginalizes over all the potential host galaxies within the GW location volume to provide a probabilistic source redshift. Here we presented H0 measurements using two new dark sirens compared to previous analyses using DECam data: GW190924$\_$021846 and GW200202$\_$154313. The photometric redshifts of the possible host galaxies of these two events are acquired from the DECam Local Volume Exploration Survey (DELVE) carried out on the Blanco telescope at Cerro Tololo. The combination of the H0 posterior from GW190924$\_$021846 and GW200202$\_$154313 together with the bright siren GW170817 leads to $H_{0} = 68.84^{+15.51}_{-7.74}\, \rm {km\, s^{-1}\, Mpc^{-1}}$. Including these two dark sirens improves the 68  per cent confidence interval (CI) by 7  per cent over GW170817 alone. This demonstrates that the addition of well-localized dark sirens in such analysis improves the precision of cosmological measurements. Using a sample containing 10 well-localized dark sirens observed during the third LIGO/Virgo observation run, without the inclusion of GW170817, we determine a measurement of $H_{0} = 76.00^{+17.64}_{-13.45}\, \rm {km\, s^{-1}\, Mpc^{-1}}$.

 

Element isotopes are characterized by distinct atomic masses and nuclear spins, which can significantly influence material properties. Notably, however, isotopes in natural materials are homogenously distributed in space. Here, we propose a method to configure material properties by repositioning isotopes in engineered van der Waals (vdW) isotopic heterostructures. We showcase the properties of hexagonal boron nitride (hBN) isotopic heterostructures in engineering confined photon-lattice waves—hyperbolic phonon polaritons. By varying the composition, stacking order, and thicknesses of h¹⁰BN and h¹¹BN building blocks, hyperbolic phonon polaritons can be engineered into a variety of energy-momentum dispersions. These confined and tailored polaritons are promising for various nanophotonic and thermal functionalities. Due to the universality and importance of isotopes, our vdW isotope heterostructuring method can be applied to engineer the properties of a broad range of materials.

 

Abstract 

Abstract