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1. Atomic Transition Probabilities for Transitions of Si i and Si ii and the Silicon Abundances of Several Very Metal-poor Stars ^∗  

   https://doi.org/10.3847/1538-4365/acb642  

   Den Hartog, E. A.; Lawler, J. E.; Sneden, C.; Roederer, I. U.; Cowan, J. J. (March 2023, The Astrophysical Journal Supplement Series)

   Abstract We report new measurements of branching fractions for 20 UV and blue lines in the spectrum of neutral silicon (Sii) originating in the 3s²3p4s³P^o_1,2,¹P^o₁, and 3s3p³¹D^o_1,2upper levels. Transitions studied include both strong, nearly pure LS multiplets as well as very weak spin-forbidden transitions connected to these upper levels. We also report a new branching fraction measurement of the⁴P_1/2–²P^o_1/2,3/2intercombination lines in the spectrum of singly ionized silicon (Siii). The weak spin-forbidden lines of Siiand Siiiprovide a stringent test on recent theoretical calculations, to which we make comparison. The branching fractions from this study are combined with previously reported radiative lifetimes to yield transition probabilities and log(gf) values for these lines. We apply these new measurements to abundance determinations in five metal-poor stars. 

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2. Mixed Signals From the Stable Isotope Composition of Precipitation and Plant Waxes in the Northern Tropical Andes

   https://doi.org/10.1029/2022JG006932  

   Pérez‐Angel, Lina C.; Sepúlveda, Julio; Montes, Camilo; Smith, Jamila J.; Molnar, Peter; González‐Arango, Catalina; Snell, Kathryn E.; Dildar, Nadia (December 2022, Journal of Geophysical Research: Biogeosciences)

   Abstract We evaluate the efficacy of the stable isotope composition of precipitation and plant waxes as proxies for paleoaltimetry and paleohydrology in the northern tropical Andes. We report monthly hydrogen (δ²H_p) and oxygen (δ¹⁸O_p) isotope values of precipitation for an annual cycle, and hydrogen isotope values of plant waxes (δ²H_wax) obtained from modern soils along the eastern and western flanks of the Eastern Cordillera of Colombia. δ²H_p, δ¹⁸O_p, as well as the unweighted mean δ²H_waxvalues ofn‐C₂₉,n‐C₃₁, andn‐C₃₃n‐alkanes in the eastern flank show a dependence on elevation (R² = 0.90, 0.82, and 0.65, respectively). In stark contrast, the stable isotope compositions of neither precipitation nor plant waxes from the western flank correlate with elevation (R² < 0.23), on top of a negligible (p‐value >0.05) correlation between δ²H_waxand δ²H_p. In general, δ²H_waxvalues along the eastern flank of the Eastern Cordillera seem to follow the trend of a simple Rayleigh distillation process that is consistent with studies elsewhere on the eastern side of the Andes in South America. Neither δ²H_pnor δ¹⁸O_p, and therefore δ²H_wax, offer reliable estimates of past elevations in the western flank, due perhaps to water vapor source mixing, evaporation overprint, contrasting plant communities, and/or differences in evapotranspiration. Thus, δ²H_waxis only reliable for paleohydrology and paleoaltimetry reconstructions on the eastern flank of the Andes, whereas interpretations based on δ²H_pand/or δ¹⁸O_pwest of the highest point of the Eastern Cordillera need to consider mixing of moisture sources in addition to precipitation amount. 

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3. New ²⁶ P(p, γ) ²⁷ S Thermonuclear Reaction Rate and Its Astrophysical Implications in the rp-process

   https://doi.org/10.3847/1538-4357/accf9c  

   Hou, S. Q.; Liu, J. B.; Trueman, T. C. L.; Li, J. G.; Pignatari, M.; Bertulani, C. A.; Xu, X. X. (June 2023, The Astrophysical Journal)

   Abstract Accurate nuclear reaction rates for²⁶P(p,γ)²⁷S are pivotal for a comprehensive understanding of therp-process nucleosynthesis path in the region of proton-rich sulfur and phosphorus isotopes. However, large uncertainties still exist in the current rate of²⁶P(p,γ)²⁷S because of the lack of nuclear mass and energy level structure information for²⁷S. We reevaluate this reaction rate using the experimentally constrained²⁷S mass, together with the shell model predicted level structure. It is found that the²⁶P(p,γ)²⁷S reaction rate is dominated by a direct capture reaction mechanism despite the presence of three resonances atE= 1.104, 1.597, and 1.777 MeV above the proton threshold in²⁷S. The new rate is overall smaller than the other previous rates from the Hauser–Feshbach statistical model by at least 1 order of magnitude in the temperature range of X-ray burst interest. In addition, we consistently update the photodisintegration rate using the new²⁷S mass. The influence of new rates of forward and reverse reaction in the abundances of isotopes produced in therp-process is explored by postprocessing nucleosynthesis calculations. The final abundance ratio of²⁷S/²⁶P obtained using the new rates is only 10% of that from the old rate. The abundance flow calculations show that the reaction path²⁶P(p,γ)²⁷S(β⁺,ν)²⁷P is not as important as previously thought for producing²⁷P. The adoption of the new reaction rates for²⁶P(p,γ)²⁷S only reduces the final production of aluminum by 7.1% and has no discernible impact on the yield of other elements. 

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4. Arabidopsis thaliana CYCLIC NUCLEOTIDE‐GATED CHANNEL2 mediates extracellular ATP signal transduction in root epidermis

   https://doi.org/10.1111/nph.17987  

   Wang, Limin; Ning, Youzheng; Sun, Jian; Wilkins, Katie A.; Matthus, Elsa; McNelly, Rose E.; Dark, Adeeba; Rubio, Lourdes; Moeder, Wolfgang; Yoshioka, Keiko; et al (February 2022, New Phytologist)

   Summary Damage can be signalled by extracellular ATP (eATP) using plasma membrane (PM) receptors to effect cytosolic free calcium ion ([Ca²⁺]_cyt) increase as a second messenger. The downstream PM Ca²⁺channels remain enigmatic. Here, theArabidopsis thalianaCa²⁺channel subunit CYCLIC NUCLEOTIDE‐GATED CHANNEL2 (CNGC2) was identified as a critical component linking eATP receptors to downstream [Ca²⁺]_cytsignalling in roots.Extracellular ATP‐induced changes in single epidermal cell PM voltage and conductance were measured electrophysiologically, changes in root [Ca²⁺]_cytwere measured with aequorin, and root transcriptional changes were determined by quantitative real‐time PCR. Twocngc2loss‐of‐function mutants were used:cngc2‐3anddefence not death1(which expresses cytosolic aequorin).Extracellular ATP‐induced transient depolarization of Arabidopsis root elongation zone epidermal PM voltage was Ca²⁺dependent, requiring CNGC2 but not CNGC4 (its channel co‐subunit in immunity signalling). Activation of PM Ca²⁺influx currents also required CNGC2. The eATP‐induced [Ca²⁺]_cytincrease and transcriptional response incngc2roots were significantly impaired.CYCLIC NUCLEOTIDE‐GATED CHANNEL2 is required for eATP‐induced epidermal Ca²⁺influx, causing depolarization leading to [Ca²⁺]_cytincrease and damage‐related transcriptional response. 

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5. Climatic stability recorded in speleothems may contribute to higher biodiversity in the Cape Floristic Region

   https://doi.org/10.1111/jbi.14592  

   Braun, Kerstin; Cowling, Richard M.; Bar‐Matthews, Miryam; Matthews, Alan; Ayalon, Avner; Zilberman, Tami; Difford, Mark; Edwards, R. Lawrence; Li, Xianglei; Marean, Curtis W. (March 2023, Journal of Biogeography)

   Abstract AimThe geography and genesis of diversity remain an enduring topic in ecology and evolution. Mediterranean Climate Ecosystems (MCEs), with their high plant diversities in winter rainfall climates, pose a challenge to popular hypotheses evoking high water availability and temperature as necessary for the evolution of high diversity. We test the hypothesis of environmental stability as a driver for the evolution of regional‐scale floristic diversity using speleothem oxygen (δ¹⁸O) and carbon (δ¹³C) isotopic values as proxies for past climatic variability in the Cape Floristic Region (CFR) and other MCEs. Locationsouth‐western Africa, California, Mediterranean Basin. TaxonPlantae. MethodsWe present new speleothem δ¹⁸O and δ¹³C records from a cave near Robertson in the western CFR. Stable isotope samples included in the analyses cover the time intervals between 240 and 670 ka BP with hiatuses at 630–500 ka and 360–310 ka. The dispersion of these stable isotope records is used as a measure for climatic variability. We compare our new analyses to speleothem records that cover full glacial and interglacial conditions in other MCEs (California and the Mediterranean Basin) as well as in eastern regions of the CFR. All sites used in this comparison have lower vascular plant biodiversity than the western CFR. ResultsAnalyses of the dispersion of the δ¹⁸O and δ¹³C datasets suggest that the highly diverse western CFR experienced climatic stability across several glacial–interglacial cycles, compared with the less diverse regions within and outside of the CFR. Main ConclusionThis result provides support for the hypothesis that lower extinction rates associated with Pleistocene biome stability may explain the higher diversity in the CFR relative to other MCEs. 

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