Identifying the Molecular Edge Termination of Exfoliated Hexagonal Boron Nitride Nanosheets with Solid-State NMR Spectroscopy and Plane-Wave DFT Calculations

Hexagonal boron nitride nanosheets (h-BNNS), the isoelectronic analog to graphene, have received interest over the past decade due to their high thermal oxidative resistance, high bandgap, catalytic activity, and low cost. The functional groups that terminate boron and nitrogen zigzag and/or armchair edges directly affect their chemical, physical, and electronic properties. However, an understanding of the molecular edge termination present in h-BNNS is lacking. Here, high-resolution magic-angle spinning (MAS) solid-state NMR (SSNMR) spectroscopy, and plane-wave density-functional theory (DFT) calculations are used to determine the molecular edge termination in exfoliated h-BNNS. 1H → 11B cross-polarization MAS (CPMAS) SSNMR spectra of h-BNNS revealed multiple hydroxyl/oxygen coordinated boron edge sites that were not detectable in direct excitation experiments. A dynamic nuclear polarization (DNP)-enhanced 1H → 15N CPMAS spectrum of h-BNNS displayed four distinct 15N resonances while a 2D 1H{14N} dipolar-HMQC spectrum acquired with fast MAS revealed three distinct 14N environments. Plane-wave DFT calculations were used to construct model edge structures and predict the corresponding 11B, 14N and 15N SSNMR spectra. Comparison of the experimental and predicted SSNMR spectra confirms that zigzag and armchair edges with both amine and boron hydroxide/oxide termination are present. The detailed characterization of h-BNNS molecular edge termination will prove useful for many material science applications. The techniques outlined here should also be applicable to understand the molecular edge terminations in other 2D materials

Variable trust in public health messaging during the first year of the COVID-19 pandemic in Southeast Alaska

Public health messaging in the United States during the COVID-19 pandemic has been variable in effectiveness. Different levels of governmental institutions have different goals and methods; it is unclear how messaging from these disparate levels is received, trusted, and implemented. We investigate the degrees of trust of Alaska Native and non-Alaska Native people in Southeast Alaska for the U.S. federal, Alaska state, and local Southeast Alaskan governments to parse how Southeast Alaskans feel about relative preparation, actions, and public health messaging. We use data collected in two waves of a regional survey: the first in April-June 2020, and the second in November 2020-February 2021. Results indicate that trust in the federal government was significantly lower than in the Alaska state government for each time period, and trust in both federal and state government significantly decreased between the two periods. Trust in the local governments of Southeast Alaska were significantly higher than both state and federal levels, and increased between the two survey waves, albeit insignificantly. We discuss potential drivers of these observations and outline how this can be leveraged for more comprehensive research into how relatively small communities with a large Native presence perceive public health messaging from different sources

Accretion of chemically fractionated material on a wide binary with a blue straggler

The components of the wide binary HIP64030=HD 113984 show a large (about 0.25 dex) iron content difference (Desidera et al.~2006 A&A 454, 581). The positions of the components on the color magnitude diagram suggest that the primary is a blue straggler. We studied the abundance difference of several elements besides iron, and we searched for stellar and substellar companions around the components to unveil the origin of the observed iron difference. A line-by-line differential abundance analysis for several elements was performed, while suitable spectral synthesis was performed for C, N, and Li. High precision radial velocities obtained with the iodine cell were combined with available literature data. The analysis of additional elements shows that the abundance difference for the elements studied increases with increasing condensation temperature, suggesting that accretion of chemically fractionated material might have occurred in the system. Alteration of C and N likely due to CNO processing is also observed. We also show that the primary is a spectroscopic binary with a period of 445 days and moderate eccentricity. The minimum mass of the companion is 0.17 Msun. Two scenarios were explored to explain the observed abundance pattern. In the first, all abundance anomalies arise on the blue straggler. If this is the case, the dust-gas separation may have been occurred in a circumbinary disk around the blue straggler and its expected white dwarf companion, as observed in several RV Tauri and post AGB binaries. In the second scenario, accretion of dust-rich material occurred on the secondary. This would also explain the anomalous carbon isotopic ratio of the secondary. Such a scenario requires that a substantial amount of mass lost by the central binary has been accreted by the wide component

Host Galaxy Properties and Offset Distributions of Fast Radio Bursts: Implications for their Progenitors

We present observations and detailed characterizations of five new host galaxies of fast radio bursts (FRBs) discovered with the Australian Square Kilometre Array Pathfinder (ASKAP) and localized to $\lesssim 1''$. Combining these galaxies with FRB hosts from the literature, we introduce criteria based on the probability of chance coincidence to define a sub-sample of 10 highly-confident associations (at $z=0.03-0.52$), three of which correspond to known repeating FRBs. Overall, the FRB host galaxies exhibit a broad, continuous range of color ($M_u-M_r = 0.9 - 2.0$), stellar mass ($M_\star = 10^{8} - 6\times 10^{10}\,M_{\odot}$), and star-formation rate (${\rm SFR} = 0.05 - 10\,M_{\odot}\,{\rm yr}^{-1}$) spanning the full parameter space occupied by $z<0.5$ galaxies. However, they do not track the color-magnitude, SFR-$M_\star$, nor BPT diagrams of field galaxies surveyed at similar redshifts. There is an excess of "green valley" galaxies and an excess of emission-line ratios indicative of a harder radiation field than that generated by star-formation alone. From the observed stellar mass distribution, we rule out the hypothesis that FRBs strictly track stellar mass in galaxies ($>99\%$ c.l.). We measure a median offset of 3.3 kpc from the FRB to the estimated center of the host galaxies and compare the host-burst offset distribution and other properties with the distributions of long- and short-duration gamma-ray bursts (LGRBs and SGRBs), core-collapse supernovae (CC-SNe), and Type Ia SNe. This analysis rules out galaxies hosting LGRBs (faint, star-forming galaxies) as common hosts for FRBs ($>95\%$ c.l.). Other transient channels (SGRBs, CC- and Type Ia SNe) have host galaxy properties and offsets consistent with the FRB distributions. All of the data and derived quantities are made publicly available on a dedicated website and repository.Comment: Accepted for publication in ApJ. All data are publicly available at https://frbhosts.org and https://github.com/FRBs/FRB. Version 2 of manuscript includes updated FRB uncertainty estimate

Host Galaxy Properties and Offset Distributions of Fast Radio Bursts: Implications for Their Progenitors

We present observations and detailed characterizations of five new host galaxies of fast radio bursts (FRBs) discovered with the Australian Square Kilometre Array Pathfinder (ASKAP) and localized to ≾ 1". Combining these galaxies with FRB hosts from the literature, we introduce criteria based on the probability of chance coincidence to define a subsample of 10 highly confident associations (at z = 0.03–0.52), 3 of which correspond to known repeating FRBs. Overall, the FRB-host galaxies exhibit a broad, continuous range of color (M_u − M_r = 0.9–2.0), stellar mass (M_★ = 10⁸ − 6 × 10¹⁰ M_⊙), and star formation rate (SFR = 0.05–10 M_⊙ yr⁻¹) spanning the full parameter space occupied by z 99% c.l.). We measure a median offset of 3.3 kpc from the FRB to the estimated center of the host galaxies and compare the host-burst offset distribution and other properties with the distributions of long- and short-duration gamma-ray bursts (LGRBs and SGRBs), core-collapse supernovae (CC-SNe), and SNe Ia. This analysis rules out galaxies hosting LGRBs (faint, star-forming galaxies) as common hosts for FRBs (>95% c.l.). Other transient channels (SGRBs, CC-, and SNe Ia) have host-galaxy properties and offsets consistent with the FRB distributions. All of the data and derived quantities are made publicly available on a dedicated website and repository

A Distant Fast Radio Burst Associated with Its Host Galaxy by the Very Large Array

We present the discovery and subarcsecond localization of a new fast radio burst (FRB) by the Karl G. Jansky Very Large Array (VLA) and realfast search system. The FRB was discovered on 2019 June 14 with a dispersion measure of 959 pc cm⁻³. This is the highest DM of any localized FRB and its measured burst fluence of 0.6 Jy ms is less than nearly all other FRBs. The source is not detected to repeat in 15 hr of VLA observing and 153 hr of CHIME/FRB observing. We describe a suite of statistical and data quality tests we used to verify the significance of the event and its localization precision. Follow-up optical/infrared photometry with Keck and Gemini associate the FRB with a pair of galaxies with r ∼ 23 mag. The false-alarm rate for radio transients of this significance that are associated with a host galaxy is roughly 3×10⁻⁴ hr⁻¹. The two putative host galaxies have similar photometric redshifts of z_(phot) ∼ 0.6, but different colors and stellar masses. Comparing the host distance to that implied by the dispersion measure suggests a modest (~ 50 pc/cm⁻³) electron column density associated with the FRB environment or host galaxy/galaxies

Mapping Obscured Star Formation in the Host Galaxy of FRB 20201124A

We present high-resolution 1.5--6 GHz Karl G. Jansky Very Large Array (VLA) and $\textit{Hubble Space Telescope}$ ($\textit{HST}$) optical and infrared observations of the extremely active repeating fast radio burst (FRB) FRB$\,$20201124A and its barred spiral host galaxy. We constrain the location and morphology of star formation in the host and search for a persistent radio source (PRS) coincident with FRB$\,$20201124A. We resolve the morphology of the radio emission across all frequency bands and measure a star formation rate SFR $\approx 8.9\,M_{\odot}$ yr$^{-1}$, a factor of $\approx 4-6$ larger than optically-inferred SFRs, demonstrating dust-obscured star formation throughout the host. Compared to a sample of all known FRB hosts with radio emission, the host of FRB$\,$20201124A has the most significant obscured star formation. While ${\it HST}$ observations show the FRB to be offset from the bar or spiral arms, the radio emission extends to the FRB location. We propose that the FRB progenitor could have formed $\textit{in situ}$ (e.g., a magnetar central engine born from the explosion of a massive star). It is still plausible, although less likely, that the progenitor of FRB$\,$20201124A migrated from the central bar of the host, e.g., via a runaway massive star. We further place a limit on the luminosity of a putative PRS at the FRB position of $L_{\rm 6.0 \ GHz}$$\lesssim$2.6$\times$$10^{27}$erg s$^{-1}$Hz$^{-1}$, two orders of magnitude below any PRS known to date. However, this limit is still broadly consistent with both magnetar nebulae and hypernebulae models assuming a constant energy injection rate of the magnetar and an age of$\gtrsim 10^{5}$ yr in each model, respectively.Comment: 21 pages, 6 figures, 3 tables, Submitte

Wafer-scale detachable monocrystalline Germanium nanomembranes for the growth of III-V materials and substrate reuse

Germanium (Ge) is increasingly used as a substrate for high-performance optoelectronic, photovoltaic, and electronic devices. These devices are usually grown on thick and rigid Ge substrates manufactured by classical wafering techniques. Nanomembranes (NMs) provide an alternative to this approach while offering wafer-scale lateral dimensions, weight reduction, limitation of waste, and cost effectiveness. Herein, we introduce the Porous germanium Efficient Epitaxial LayEr Release (PEELER) process, which consists of the fabrication of wafer-scale detachable monocrystalline Ge NMs on porous Ge (PGe) and substrate reuse. We demonstrate monocrystalline Ge NMs with surface roughness below 1 nm on top of nanoengineered void layer enabling layer detachment. Furthermore, these Ge NMs exhibit compatibility with the growth of III-V materials. High-resolution transmission electron microscopy (HRTEM) characterization shows Ge NMs crystallinity and high-resolution X-ray diffraction (HRXRD) reciprocal space mapping endorses high-quality GaAs layers. Finally, we demonstrate the chemical reconditioning process of the Ge substrate, allowing its reuse, to produce multiple free-standing NMs from a single parent wafer. The PEELER process significantly reduces the consumption of Ge during the fabrication process which paves the way for a new generation of low-cost flexible optoelectronics devices.Comment: 17 pages and 6 figures along with 3 figures in supporting informatio

Performance of CMS muon reconstruction in pp collision events at sqrt(s) = 7 TeV

The performance of muon reconstruction, identification, and triggering in CMS has been studied using 40 inverse picobarns of data collected in pp collisions at sqrt(s) = 7 TeV at the LHC in 2010. A few benchmark sets of selection criteria covering a wide range of physics analysis needs have been examined. For all considered selections, the efficiency to reconstruct and identify a muon with a transverse momentum pT larger than a few GeV is above 95% over the whole region of pseudorapidity covered by the CMS muon system, abs(eta) < 2.4, while the probability to misidentify a hadron as a muon is well below 1%. The efficiency to trigger on single muons with pT above a few GeV is higher than 90% over the full eta range, and typically substantially better. The overall momentum scale is measured to a precision of 0.2% with muons from Z decays. The transverse momentum resolution varies from 1% to 6% depending on pseudorapidity for muons with pT below 100 GeV and, using cosmic rays, it is shown to be better than 10% in the central region up to pT = 1 TeV. Observed distributions of all quantities are well reproduced by the Monte Carlo simulation.Comment: Replaced with published version. Added journal reference and DO