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1. Theoretical Analysis of Critical Conditions for Crack Formation and Propagation, and Optimal Operation of SOECs

   https://doi.org/10.1149/1945-7111/ac5fee  

   Wang, Yudong ; Virkar, Anil V. ; Khonsari, M. M. ; Zhou, Xiao-Dong ( April 2022 , Journal of The Electrochemical Society)

   A theoretical analysis on crack formation and propagation was performed based on the coupling between the electrochemical process, classical elasticity, and fracture mechanics. The chemical potential of oxygen, thus oxygen partial pressure, at the oxygen electrode-electrolyte interface (${\mu }_{O_2}^{\mathit{OE\mid El}}$) was investigated as a function of transport properties, electrolyte thickness and operating conditions (e.g., steam concentration, constant current, and constant voltage). Our analysis shows that: a lower ionic area specific resistance (ASR),$r_i^{OE},$and a higher electronic ASR ($r_e^{OE}$) of the oxygen electrode/electrolyte interface are in favor of suppressing crack formation. The${\mu }_{O_2}^{OE\mid El},$thus local pO₂, are sensitive towards the operating parameters under galvanostatic or potentiostatic electrolysis. Constant current density electrolysis provides better robustness, especially at a high current density with a high steam content. While constant voltage electrolysis leads to greater variations of${\mu }_{O_2}^{OE\mid El}.$Constant current electrolysis, however, is not suitable for an unstable oxygen electrode because${\mu }_{O_2}^{OE\mid El}$can reach a very high value with a gradually increased$r_i^{OE}.$A crack may only occur under certain conditions when$p_{O_2}^{TPB}>p_{cr}.$

    

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2. Two of a Kind: Comparing Big and Small Black Holes in Binaries with Gravitational Waves

   https://doi.org/10.3847/1538-4357/ad0558  

   Farah, Amanda M. ; Fishbach, Maya ; Holz, Daniel E. ( February 2024 , The Astrophysical Journal)

   When modeling the population of merging binary black holes, analyses have generally focused on characterizing the distribution of primary (i.e., more massive) black holes in the binary, while using simplistic prescriptions for the distribution of secondary masses. However, the secondary mass distribution and its relationship to the primary mass distribution provide a fundamental observational constraint on the formation history of coalescing binary black holes. If both black holes experience similar stellar evolutionary processes prior to collapse, as might be expected in dynamical formation channels, the primary and secondary mass distributions would show similar features. If they follow distinct evolutionary pathways (for example, due to binary interactions that break symmetry between the initially more massive and less massive stars), their mass distributions may differ. We present the first analysis of the binary black hole population that explicitly fits for the secondary mass distribution. We find that the data is consistent with a ∼30M_⊙peak existing only in the distribution of secondary rather than primary masses. This would have major implications for our understanding of the formation of these binaries. Alternatively, the data is consistent with the peak existing in both component mass distributions, a possibility not included in most previous studies. In either case, the peak is observed at${31.4}_{-2.6}^{+2.3}{M}_{\odot }$, which is shifted lower than the value obtained in previous analyses of the marginal primary mass distribution, placing this feature in further tension with expectations from a pulsational pair-instability supernova pileup.

    

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3. Sum frequency generation, calculation of absolute intensities, comparison with experiments, and two-field relaxation-based derivation

   https://doi.org/10.1073/pnas.1906243117  

   Niu, Kai ; Marcus, Rudolph A. ( January 2020 , Proceedings of the National Academy of Sciences)

   The experimental sum frequency generation (SFG) spectrum is the response to an infrared pulse and a visible pulse and is a highly surface-sensitive technique. We treat the surface dangling OH bonds at the air/water interface and focus on the absolute SFG intensities for the resonant terms, a focus that permits insight into the consequences of some approximations. For the polarization combinations, the calculated linewidths for the water interface dangling OH SFG band at 3,700${\mathrm{c}\mathrm{m}}^{-1}$are, as usual, too large, because of the customary neglect of motional narrowing. The integrated spectrum is used to circumvent this problem and justified here using a Kubo-like formalism and theoretical integrated band intensities rather than peak intensities. Only relative SFG intensities are usually reported. The absolute integrated SFG intensities for three polarization combinations for sum frequency, visible, and infrared beams are computed. We use molecular dynamics and the dipole and the polarizability matrix elements obtained from infrared and Raman studies of${\mathrm{H}}_2$O vapor. The theoretical expressions for two of the absolute susceptibilities contain only a single term and agree with experiment to about a factor of 1.3, with no adjustable parameters. The Fresnel factors are included in that comparison. One of the susceptibilities contains instead four positive and negative terms and agrees less well. The expression for the SFG correlation function is normally derived from a statistical mechanical formulation using a time-evolving density matrix. We show how a derivation based on a two-field relaxation leads to the same final result.

    

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4. Characterizing the fundamental bending vibration of a linear polyatomic molecule for symmetry violation searches

   https://doi.org/10.1088/1367-2630/ace471  

   Jadbabaie, Arian ; Takahashi, Yuiki ; Pilgram, Nickolas H ; Conn, Chandler J ; Zeng, Yi ; Zhang, Chi ; Hutzler, Nicholas R ( July 2023 , New Journal of Physics)

   Polyatomic molecules have been identified as sensitive probes of charge-parity violating and parity violating physics beyond the Standard Model (BSM). For example, many linear triatomic molecules are both laser-coolable and have parity doublets in the ground electronic$\tilde{X}{}^2{\mathrm{\Sigma }}^{+}(010)$state arising from the bending vibration, both features that can greatly aid BSM searches. Understanding the$\tilde{X}{}^2{\mathrm{\Sigma }}^{+}(010)$state is a crucial prerequisite to precision measurements with linear polyatomic molecules. Here, we characterize the fundamental bending vibration of${}^{174}$YbOH using high-resolution optical spectroscopy on the nominally forbidden$\tilde{X}{}^2{\mathrm{\Sigma }}^{+}(010)$$\to \tilde{A}{}^2{\mathrm{\Pi }}_{1/2}(000)$transition at 588 nm. We assign 39 transitions originating from the lowest rotational levels of the$\tilde{X}{}^2{\mathrm{\Sigma }}^{+}(010)$state, and accurately model the state’s structure with an effective Hamiltonian using best-fit parameters. Additionally, we perform Stark and Zeeman spectroscopy on the$\tilde{X}{}^2{\mathrm{\Sigma }}^{+}(010)$state and fit the molecule-frame dipole moment to$D_{\mathrm{m}\mathrm{o}\mathrm{l}}=2.16(1)$Dand the effective electrong-factor to$g_S=2.07(2)$. Further, we use an empirical model to explain observed anomalous line intensities in terms of interference from spin–orbit and vibronic perturbations in the excited$\tilde{A}{}^2{\mathrm{\Pi }}_{1/2}(000)$state. Our work is an essential step toward searches for BSM physics in YbOH and other linear polyatomic molecules.

    

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5. Patchy Kinetic Sunyaev–Zel’dovich Effect with Controlled Reionization History and Morphology

   https://doi.org/10.3847/1538-4357/ac8481  

   Chen, Nianyi ; Trac, Hy ; Mukherjee, Suvodip ; Cen, Renyue ( February 2023 , The Astrophysical Journal)

   Using the novel semi-numerical code for reionization AMBER, we model the patchy kinetic Sunyaev–Zel’dovich (kSZ) effect by directly specifying the reionization history with the redshift midpointz_mid, duration Δ_z, and asymmetryA_z. We further control the ionizing sources and radiation through the minimum halo massM_hand the radiation mean free pathλ_mfp. AMBER reproduces the free-electron number density and the patchy kSZ power spectrum of radiation–hydrodynamic simulations at the target resolution (1 Mpch⁻¹) with matched reionization parameters. With a suite of (2 Gpc/h)³simulations using AMBER, we first constrain the redshift midpoint 6.0 <z_mid< 8.9 using the Planck 2018 Thomson optical depth result (95% CL). Then, assumingz_mid= 8, we find that the amplitude of$D_{\mathit{\ell }=3000}^{\mathrm{pkSZ}}$scales linearly with the duration of reionization Δ_zand is consistent with the 1σupper limit from South Pole Telescope (SPT) results up to Δ_z< 5.1 (Δ_zencloses 5%–95% ionization). Moreover, a shorterλ_mfpcan lead to a ∼10% lower$D_{\mathit{\ell }=3000}^{\mathrm{pkSZ}}$and a flatter slope in the$D_{\mathit{\ell }=3000}^{\mathrm{pkSZ}}-{\mathrm{\Delta }}_z$scaling relation, thereby affecting the constraints on Δ_zatℓ= 3000. Allowingz_midandλ_mfpto vary simultaneously, we get spectra consistent with the SPT result (95% CL) up to Δ_z= 12.8 (butA_z> 8 is needed to ensure the end of reionization beforez= 5.5). We show that constraints on the asymmetry require ∼0.1μk²measurement accuracy at multipoles other thanℓ= 3000. Finally, we find that the amplitude and shape of the kSZ spectrum are only weakly sensitive toM_hunder a fixed reionization history and radiation mean free path.

    

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