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1. Electron impact excitation of allowed and forbidden transitions between fine-structure levels in Ti III

   https://doi.org/10.1088/1361-6595/ad95b8  

   Wang, Yang; Cao, Qiu-Yao; Zhu, Xi-Ming; Du, Chun-Meng; Bartschat, Klaus (November 2024, Plasma Sources Science and Technology)

   Abstract Introduction: We present an extensive theoretical investigation of the electron impact excitation of doubly-ionized titanium (Ti III) to meet the needs of spectral analysis and plasma modeling. OBJECTIVES: The main objective of this work is to extend the currently scarce database of both structure and collision data for Ti III. METHODS: The calculation was performed in the close-coupling approximation using theB-splineR-matrix method. The multi-configuration Hartree–Fock method in combination withB-spline configuration interaction expansions and the non-orthogonal orbitals technique is employed for accurate descriptions of the target wave functions and adequate accounts of the various interactions between the target states. Relativistic effects are treated at the semi-relativistic Breit-Pauli approximation level. RESULTS: The present close-coupling expansion includes 138 fine-structure levels of Ti III belonging to the $3d^2$, $4s^2$, $4s4p$, $3d4l$( $l=0-3$), $3d5l$( $l=0-3$), $3d6s$, and $3d6p$configurations. Comprehensive sets of radiative and electron collisional data are reported for all of the possible transitions between the 138 fine-structure levels. Thermally averaged collision strengths are determined using a Maxwellian distribution for a wide range of temperatures from ${10}^2$K to ${10}^5$K. The accuracy of the calculated radiative parameters is validated by comparing with available values from the NIST database and previous literature. CONCLUSION: Given the lack of sufficient currently available experimental and theoretical data, the electron impact excitation cross sections of the Ti III fine-structure levels presented here are systematic, extensive, and internally consistent, thus making them suitable for many modeling applications. 

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2. Structural phase purification of bulk HfO ₂ :Y through pressure cycling

   https://doi.org/10.1073/pnas.2312571121  

   Musfeldt, J. L.; Singh, Sobhit; Fan, Shiyu; Gu, Yanhong; Xu, Xianghan; Cheong, S.-W.; Liu, Z.; Vanderbilt, David; Rabe, Karin M. (January 2024, Proceedings of the National Academy of Sciences)

   We combine synchrotron-based infrared absorption and Raman scattering spectroscopies with diamond anvil cell techniques and first-principles calculations to explore the properties of hafnia under compression. We find that pressure drives HfO ${}_2$:7%Y from the mixed monoclinic ( $P{2}_1/c$) $+$antipolar orthorhombic ( $\mathit{Pbca}$) phase to pure antipolar orthorhombic ( $\mathit{Pbca}$) phase at approximately 6.3 GPa. This transformation is irreversible, meaning that upon release, the material is kinetically trapped in the $\mathit{Pbca}$metastable state at 300 K. Compression also drives polar orthorhombic ( $Pca{2}_1$) hafnia into the tetragonal ( $P{4}_2/nmc$) phase, although the latter is not metastable upon release. These results are unified by an analysis of the energy landscape. The fact that pressure allows us to stabilize targeted metastable structures with less Y stabilizer is important to preserving the flat phonon band physics of pure HfO ${}_2$. 

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3. Global reconstruction reduces the uncertainty of oceanic nitrous oxide emissions and reveals a vigorous seasonal cycle

   https://doi.org/10.1073/pnas.1921914117  

   Yang, Simon; Chang, Bonnie X.; Warner, Mark J.; Weber, Thomas S.; Bourbonnais, Annie M.; Santoro, Alyson E.; Kock, Annette; Sonnerup, Rolf E.; Bullister, John L.; Wilson, Samuel T.; et al (May 2020, Proceedings of the National Academy of Sciences)

   Assessment of the global budget of the greenhouse gas nitrous oxide ( ${\mathrm{N}}_2$O) is limited by poor knowledge of the oceanic ${\mathrm{N}}_2$O flux to the atmosphere, of which the magnitude, spatial distribution, and temporal variability remain highly uncertain. Here, we reconstruct climatological ${\mathrm{N}}_2$O emissions from the ocean by training a supervised learning algorithm with over 158,000 ${\mathrm{N}}_2$O measurements from the surface ocean—the largest synthesis to date. The reconstruction captures observed latitudinal gradients and coastal hot spots of ${\mathrm{N}}_2$O flux and reveals a vigorous global seasonal cycle. We estimate an annual mean ${\mathrm{N}}_2$O flux of 4.2 ± 1.0 Tg N $\cdot {\mathrm{y}}^{-1}$, 64% of which occurs in the tropics, and 20% in coastal upwelling systems that occupy less than 3% of the ocean area. This ${\mathrm{N}}_2$O flux ranges from a low of 3.3 ± 1.3 Tg N $\cdot {\mathrm{y}}^{-1}$in the boreal spring to a high of 5.5 ± 2.0 Tg N $\cdot {\mathrm{y}}^{-1}$in the boreal summer. Much of the seasonal variations in global ${\mathrm{N}}_2$O emissions can be traced to seasonal upwelling in the tropical ocean and winter mixing in the Southern Ocean. The dominant contribution to seasonality by productive, low-oxygen tropical upwelling systems (>75%) suggests a sensitivity of the global ${\mathrm{N}}_2$O flux to El Niño–Southern Oscillation and anthropogenic stratification of the low latitude ocean. This ocean flux estimate is consistent with the range adopted by the Intergovernmental Panel on Climate Change, but reduces its uncertainty by more than fivefold, enabling more precise determination of other terms in the atmospheric ${\mathrm{N}}_2$O budget. 

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4. A Pride of Satellites in the Constellation Leo? Discovery of the Leo VI Milky Way Satellite Ultra-faint Dwarf Galaxy with DELVE Early Data Release 3

   https://doi.org/10.3847/1538-4357/ad9b0c  

   Tan, C_Y; Cerny, W.; Drlica-Wagner, A.; Pace, A_B; Geha, M.; Ji, A_P; Li, T_S; Adamów, M.; Anbajagane, D.; Bom, C_R; et al (January 2025, The Astrophysical Journal)

   Abstract We report the discovery and spectroscopic confirmation of an ultra-faint Milky Way satellite in the constellation of Leo. This system was discovered as a spatial overdensity of resolved stars observed with Dark Energy Camera (DECam) data from an early version of the third data release of the DECam Local Volume Exploration (or DELVE) survey. The low luminosity ( $M_V=-3.56_{-0.37}^{+0.47}$; $L_V=2300_{-700}^{+1200}{L}_{\odot }$), large size ( $R_{1/2}=90_{-30}^{+30}$pc), and large heliocentric distance ( $D=111_{-6}^{+9}$kpc) are all consistent with the population of ultra-faint dwarf galaxies (UFDs). Using Keck/DEIMOS observations of the system, we were able to spectroscopically confirm nine member stars, while measuring a tentative mass-to-light ratio of $700_{-500}^{+1400}{M}_{\odot }/L_{\odot }$and a nonzero metallicity dispersion of ${\sigma }_{[\mathrm{Fe}/\mathrm{H}]}=0.19_{-0.11}^{+0.14}$, further confirming Leo VI’s identity as a UFD. While the system has a highly elliptical shape, $ϵ=0.54_{-0.29}^{+0.19}$, we do not find any conclusive evidence that it is tidally disrupting. Moreover, despite the apparent on-sky proximity of Leo VI to members of the proposed Crater-Leo infall group, its smaller heliocentric distance and inconsistent position in energy–angular momentum space make it unlikely that Leo VI is part of the proposed infall group. 

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5. 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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