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  1. Free, publicly-accessible full text available December 6, 2023
  2. ABSTRACT TIC 470710327, a massive compact hierarchical triple-star system, was recently identified by NASA’s Transiting Exoplanet Survey Satellite. TIC 470710327 is comprised of a compact (1.10 d) circular eclipsing binary, with total mass $\approx 10.9\!-\!13.2\, \rm {M_{\odot }}$, and a more massive $\approx 14\!-\!17\, \rm {M_{\odot }}$ eccentric non-eclipsing tertiary in a 52.04 d orbit. Here, we present a progenitor scenario for TIC 470710327 in which ‘2 + 2’ quadruple dynamics result in Zeipel–Lidov–Kozai oscillations that lead to a contact phase of the more massive binary. In this scenario, the two binary systems should form in a very similar manner, and dynamics trigger the merger of the more massive binary either during late phases of star formation or several Myr after the zero-age main sequence, when the stars begin to expand. Any evidence that the tertiary is a highly magnetized (∼1–10 kG), slowly rotating blue main-sequence star would hint towards a quadruple origin. Finally, our scenario suggests that the population of inclined compact multiple-stellar systems is reduced into coplanar systems, via mergers, late during star formation or early in the main sequence. The elucidation of the origin of TIC 470710327 is crucial in our understanding of multiple massive star formation and evolution.
    Free, publicly-accessible full text available July 19, 2023
  3. Kinematic distance determinations are complicated by a kinematic distance ambiguity (KDA) within the Solar orbit. For an axisymmetric Galactic rotation model, two distances, a "near" and "far" distance, have the same radial velocity. Formaldehyde (H2CO) absorption measurements have been used to resolve the KDA toward Galactic HII regions. This method relies on the detection of H2CO absorption against the broadband radio continuum emission from HII regions. H2CO absorption at velocities between the HII region velocity and the maximum velocity along the line of sight (the tangent point velocity) implies that the HII region lies at the far kinematic distance whereas a lack of absorption implies that it lies at the near kinematic distance. The reliability of KDA resolutions using H2CO is unclear, however, as disagreements between distances derived using H2CO absorption and those derived using other methods are common. Here we use new H2CO and radio recombination line data from the Green Bank Telescope (GBT) Diffuse Ionized Gas Survey (GDIGS) to test whether H2CO absorption measurements can accurately resolve the KDA for 44 Galactic HII regions that have known distances from maser parallax measurements. For each of the 44 HII regions we determine whether the parallax distance is consistent withmore »either the near or the far kinematic distance. We find that the Galactic distribution of H2CO is too sparse to reliably determine whether an HII region is at its near kinematic distance. The H2CO method also incorrectly resolves the KDA for 80% of HII regions that it places at the far kinematic distance; in such cases H2CO absorption may be caused by other sources of radio continuum emission (possibly the CMB, diffuse free-free, or synchrotron). Our results indicate that the H2CO method is unsuitable to resolve the KDA toward Galactic HII regions.« less
    Free, publicly-accessible full text available June 29, 2023
  4. Abstract

    The prevailing view of intracellular RNA trafficking in eukaryotic cells is that RNAs transcribed in the nucleus either stay in the nucleus or cross the nuclear envelope, entering the cytoplasm for function. However, emerging evidence illustrates that numerous functional RNAs move in the reverse direction, from the cytoplasm to the nucleus. The mechanism underlying RNA nuclear import has not been well elucidated. Viroids are single-stranded circular noncoding RNAs that infect plants. Using Nicotiana benthamiana, tomato (Solanum lycopersicum), and nuclear-replicating viroids as a model, we showed that cellular IMPORTIN ALPHA-4 (IMPa-4) is likely involved in viroid RNA nuclear import, empirically supporting the involvement of Importin-based cellular pathway in RNA nuclear import. We also confirmed the involvement of a cellular protein (viroid RNA-binding protein 1 [VIRP1]) that binds both IMPa-4 and viroids. Moreover, a conserved C-loop in nuclear-replicating viroids serves as a key signal for nuclear import. Disrupting C-loop impairs VIRP1 binding, viroid nuclear accumulation, and infectivity. Further, C-loop exists in a subviral satellite noncoding RNA that relies on VIRP1 for nuclear import. These results advance our understanding of subviral RNA infection and the regulation of RNA nuclear import.

  5. Multi-principal element alloys (MPEAs) with remarkable performances possess great potential as structural, functional, and smart materials. However, their efficient performance-orientated design in a wide range of compositions and types is an extremely challenging issue, because of properties strongly dependent upon the composition and composition-dominated microstructure. Here, we propose a multistage-design approach integrating machine learning, physical laws and a mathematical model for developing the desired-property MPEAs in a very time-efficient way. Compared to the existing physical model- or machine-learning-assisted material development, the forward-and-inverse problems, including identifying the target property and unearthing the optimal composition, can be tackled with better efficiency and higher accuracy using our proposed avenue, which defeats the one-step component-performance design strategy by multistage-design coupling constraints. Furthermore, we developed a new multi-phase MPEA at the minimal time and cost, whose high strength-ductility synergy exceeded those of its system and subsystem reported so far by searching for the optimal combination of phase fraction and composition. The present work suggests that the property-guided composition and microstructure are precisely tailored through the newly built approach with significant reductions of the development period and cost, which is readily extendable to other multi-principal element materials.
    Free, publicly-accessible full text available May 10, 2023
  6. Free, publicly-accessible full text available March 1, 2023
  7. Free, publicly-accessible full text available September 26, 2023
  8. Free, publicly-accessible full text available February 1, 2023
  9. ABSTRACT

    We study the long-term orbital evolution of stars around a merging massive or supermassive black hole binary (BHB), taking into account the general relativistic effect induced by the black hole (BH) spin. When the BH spin is significant compared to and misaligned with the binary orbital angular momentum, the orbital axis ($\hat{\boldsymbol {l}}$) of the circumbinary star can undergo significant evolution during the binary orbital decay driven by gravitational radiation. Including the spin effect of the primary (more massive) BH, we find that starting from nearly coplanar orbital orientations, the orbital axes $\hat{\boldsymbol {l}}$ of circumbinary stars preferentially evolve towards the spin direction after the merger of the BHB, regardless of the initial BH spin orientation. Such alignment phenomenon, i.e. small final misalignment angle between $\hat{\boldsymbol {l}}$ and the spin axis of the remnant BH $\hat{\boldsymbol {S}}$, can be understood analytically using the principle of adiabatic invariance. For the BHBs with extremely mass ratio (m2/m1 ≲ 0.01), $\hat{\boldsymbol {l}}$ may experience more complicated evolution as adiabatic invariance breaks down, but the trend of alignment still works reasonably well when the initial binary spin–orbit angle is relatively small. Our result suggests that the correlation between the orientations of stellar orbitsmore »and the spin axis of the central BH could provide a potential signature of the merger history of the massive BH.

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  10. Nitrogen doping in carbon materials can modify the employed carbon material’s electronic and structural properties, which helps in creating a stronger metal-support interaction. In this study, the role of nitrogen doping in improving the durability of Pt catalysts supported on a three-dimensional vertically aligned carbon nanofiber (VACNF) array towards oxygen reduction reaction (ORR) was explored. The nitrogen moieties present in the N-VACNF enhanced the metal-support interaction and contributed to a reduction in the Pt particle size from 3.1 nm to 2.3 nm. The Pt/N-VACNF catalyst showed better durability when compared to Pt/VACNF and Pt/C catalysts with similar Pt loading. DFT calculations validated the increase in the durability of the Pt NPs with an increase in pyridinic N and corroborated the molecular ORR pathway for Pt/N-VACNF. Moreover, the Pt/N-VACNF catalyst was found to have excellent tolerance towards methanol crossover.
    Free, publicly-accessible full text available December 1, 2022