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1. Environments of dolomitization and evolution of carbonate diagenesis in the Triassic Zhenfeng margin of the Yangtze Platform in the Nanpanjiang Basin, South China

   Bradley, George; Luczaj, John; Lehrmann, Dan (April 2024, Geological Society of America Abstracts with Program)

   The Yangtze Platform borders the Nanpanjiang Basin on its north and west. During the Early Triassic the platform evolved from low-relief ramp with oolitic margins to a steepening platform with a relatively flat-topped geometry with margin shoals and evaporitic interior facies. At the Zhenfeng margin the precursor depositional facies include: oolitic grainstone to packstone, skeletal peloidal packstone, clotted microbialites and fenestral laminites. The Anshun strata range from undolomitized to partially dolomitized oolite and microbial facies to partially and completely dolomitized facies such as fenestral laminites. Dolomitization changes upward through the section with fenestral laminate facies being more pervasively dolomitized than the oolitic and skeletal packstone facies. The diagenetic evolution (paragenetic sequence includes: neomorphic alteration of aragonite, marine cementation, replacement dolomite, euherdral dolomites, saddle dolomites, calcite veins, stylolites, and late-stage fractures with calcite and oxide fill. Previous data from the Yangtze Platform include dolomite showing δ¹⁸O values ranging from -7.7‰ to 0.75‰ (VPDB) and δ ¹³C values ranging from 0.77‰ to 4.0‰ (VPDB). Vein calcite values range from δ ¹⁸O -18.4‰ to -5.2‰ and δ ¹³C -6.1 to 3.4‰. ⁸⁷Sr/⁸⁶Sr values from dolomite ranges from 0.707677 to 0.708601 with the exception of elevated ⁸⁷Sr/⁸⁶Sr in three samples. Homogenization temperatures (Th) and freezing point depressions (Tmice) from primary fluid inclusion assemblages from dolomite crystals indicate entrapment of saline brines (9.5 to 16 wt. % NaCl) over temperatures of 80-185°C. The preferential dolomitization of mud-rich platform interior facies and preservation of oolitic limestone facies at the platform margin points to interior derived dolomitizing fluids consistent with evaporative reflux. The range in δ ¹⁸O is consistent with enrichment by evaporative concentration of seawater, but also includes negative values consistent with high temperature fluids. ⁸⁷Sr/⁸⁶Sr values in dolomite are consistent with modified seawater including a radiogenic contribution of hydrothermal fluids. The geothermometric data, oxygen isotope values and radiogenic Sr contribution indicates that early dolomites were recrystallized at high temperatures by burial fluids. 

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2. Effect of Au substrate and coating on the lasing characteristics of GaAs nanowires

   https://doi.org/10.1038/s41598-021-00855-w  

   Aman, Gyanan; Mohammadi, Fatemesadat; Fränzl, Martin; Lysevych, Mykhaylo; Tan, Hark Hoe; Jagadish, Chennupati; Schmitzer, Heidrun; Cahay, Marc; Wagner, Hans Peter (December 2021, Scientific Reports)

   Abstract Optically pumped lasing from highly Zn-doped GaAs nanowires lying on an Au film substrate and from Au-coated nanowires has been demonstrated up to room temperature. The conically shaped GaAs nanowires were first coated with a 5 nm thick Al 2 O 3 shell to suppress atmospheric oxidation and band-bending effects. Doping with a high Zn concentration increases both the radiative efficiency and the material gain and leads to lasing up to room temperature. A detailed analysis of the observed lasing behavior, using finite-difference time domain simulations, reveals that the lasing occurs from low loss hybrid modes with predominately photonic character combined with electric field enhancement effects. Achieving low loss lasing from NWs on an Au film and from Au coated nanowires opens new prospects for on-chip integration of nanolasers with new functionalities including electro-optical modulation, conductive shielding, and polarization control. 

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3. The Hubble Constant from Infrared Surface Brightness Fluctuation Distances*

   https://doi.org/10.3847/1538-4357/abe86a  

   Blakeslee, John P.; Jensen, Joseph B.; Ma, Chung-Pei; Milne, Peter A.; Greene, Jenny E. (April 2021, The Astrophysical Journal)

   Abstract We present a measurement of the Hubble constantH₀from surface brightness fluctuation (SBF) distances for 63 bright, mainly early-type galaxies out to 100 Mpc observed with the WFC3/IR on the Hubble Space Telescope (HST). The sample is drawn from several independent HST imaging programs using the F110W bandpass, with the majority of the galaxies being selected from the MASSIVE survey. The distances reach the Hubble flow with a median statistical uncertainty per measurement of 4%. We construct the Hubble diagram with these IR SBF distances and constrainH₀using four different treatments of the galaxy velocities. For the SBF zero-point calibration, we use both the existing tie to Cepheid variables, updated for consistency with the latest determination of the distance to the Large Magellanic Cloud from detached eclipsing binaries, and a new tie to the tip of the red giant branch (TRGB) calibrated from the maser distance to NGC 4258. These two SBF calibrations are consistent with each other and with theoretical predictions from stellar population models. From a weighted average of the Cepheid and TRGB calibrations, we deriveH₀= 73.3 ± 0.7 ± 2.4 km s⁻¹Mpc⁻¹, where the error bars reflect the statistical and systematic uncertainties. This result accords well with recent measurements ofH₀from Type Ia supernovae, time delays in multiply lensed quasars, and water masers. The systematic uncertainty could be reduced to below 2% by calibrating the SBF method with precision TRGB distances for a statistical sample of massive early-type galaxies out to the Virgo cluster measured with the James Webb Space Telescope. 

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4. Triple Oxygen (δ18O, Δ17O), Hydrogen (δ2H), and Iron (δ56Fe) Stable Isotope Signatures Indicate a Silicate Magma Source and Magmatic-Hydrothermal Genesis for Magnetite Orebodies at El Laco, Chile

   https://doi.org/10.5382/econgeo.4760  

   Childress, T. (November 2020, Economic geology)

   null (Ed.)

   The Plio-Pleistocene El Laco iron oxide-apatite (IOA) orebodies in northern Chile are some of the most enigmatic mineral deposits on Earth, interpreted to have formed as lava flows or by hydrothermal replacement, two radically different processes. Field observations provide some support for both processes, but ultimately fail to explain all observations. Previously proposed genetic models based on observations and study of outcrop samples include (1) magnetite crystallization from an erupting immiscible Fe- and P-rich (Si-poor) melt and (2) metasomatic replacement of andesitic lava flows by a hypogene hydrothermal fluid. A more recent investigation of outcrop and drill core samples at El Laco generated data that were used to develop a new genetic model that invokes shallow emplacement and surface venting of a magnetite-bearing magmatic-hydrothermal fluid suspension. This fluid, with rheological properties similar to basaltic lava, would have been mobilized by decompression- induced collapse of the volcanic edifice. In this study, we report oxygen, including 17O, hydrogen, and iron stable isotope ratios in magnetite and bulk iron oxide (magnetite with minor secondary hematite and minor goethite) from five of seven orebodies around the El Laco volcano, excluding San Vicente Bajo and the minor Laquito deposits. Calculated values of δ18O, Δ17O, δD, and δ56Fe fingerprint the source of the ore-forming fluid(s): Δ17Osample = δ17Osample – δ18Osample * 0.5305. Magnetite and bulk iron oxide (magnetite variably altered to goethite and hematite) from Laco Sur, Cristales Grandes, and San Vicente Alto yield δ18O values that range from 4.3 to 4.5‰ (n = 5), 3.0 to 3.9‰ (n = 5), and –8.5 to –0.5‰ (n = 5), respectively. Magnetite samples from Rodados Negros are the least altered samples and were also analyzed for 17O as well as conventional 16O and 18O, yielding calculated δ18O values that range from 2.6 to 3.8‰ (n = 9) and Δ17O values that range from –0.13 to –0.07‰ (n = 5). Bulk iron oxide from Laco Norte yielded δ18O values that range from –10.2 to +4.5‰ (avg = 0.8‰, n = 18). The δ2H values of magnetite and bulk iron oxide from all five orebodies range from –192.8 to –79.9‰ (n = 28); hydrogen is present in fluid inclusions in magnetite and iron oxide, and in minor goethite. Values of δ56Fe for magnetite and bulk iron oxide from all five orebodies range from 0.04 to 0.70‰ (avg = 0.29‰, σ = 0.15‰, n = 26). The iron and oxygen isotope data are consistent with a silicate magma source for iron and oxygen in magnetite from all sampled El Laco orebodies. Oxygen (δ18O Δ +4.4 to –10.2‰) and hydrogen (δ 2H ≃ –79.9 to –192.8‰) stable isotope data for bulk iron oxide samples that contain minor goethite from Laco Norte and San Vicente Alto reveal that magnetite has been variably altered to meteoric values, consistent with goethite in equilibrium with local δ18O and δ2H meteoric values of ≃ –15.4 and –211‰, respectively. The H2O contents of iron oxide samples from Laco Norte and San Vicente Alto systematically increase with increasing abundance of goethite and decreasing values of δ18O and δ2H. The values of δ2H (≃ –88 to –140‰) and δ18O (3.0–4.5‰) for magnetite samples from Cristales Grandes, Laco Sur, and Rodados Negros are consistent with growth of magnetite from a degassing silicate melt and/or a boiling magmatic-hydrothermal fluid; the latter is also consistent with δ18O values for quartz, and salinities and homogenization temperatures for fluid inclusions trapped in apatite and clinopyroxene coeval with magnetite. The sum of the data unequivocally fingerprint a silicate magma as the source of the ore fluids responsible for mineralization at El Laco and are consistent with a model that explains mineralization as the synergistic result of common magmatic and magmatic-hydrothermal processes during the evolution of a caldera-related explosive volcanic system. 

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5. Understanding muscle function during perturbed in vivo locomotion using a muscle avatar approach

   https://doi.org/10.1242/jeb.244721  

   Rice, Nicole; Bemis, Caitlin M.; Daley, Monica A.; Nishikawa, Kiisa (July 2023, Journal of Experimental Biology)

   ABSTRACT The work loop technique has provided key insights into in vivo muscle work and power during steady locomotion. However, for many animals and muscles, ex vivo experiments are not feasible. In addition, purely sinusoidal strain trajectories lack variations in strain rate that result from variable loading during locomotion. Therefore, it is useful to develop an ‘avatar’ approach in which in vivo strain and activation patterns from one muscle are replicated in ex vivo experiments on a readily available muscle from an established animal model. In the present study, we used mouse extensor digitorum longus (EDL) muscles in ex vivo experiments to investigate in vivo mechanics of the guinea fowl lateral gastrocnemius (LG) muscle during unsteady running on a treadmill with obstacle perturbations. In vivo strain trajectories from strides down from obstacle to treadmill, up from treadmill to obstacle, strides with no obstacle and sinusoidal strain trajectories at the same amplitude and frequency were used as inputs in work loop experiments. As expected, EDL forces produced with in vivo strain trajectories were more similar to in vivo LG forces (R2=0.58–0.94) than were forces produced with the sinusoidal trajectory (average R2=0.045). Given the same stimulation, in vivo strain trajectories produced work loops that showed a shift in function from more positive work during strides up from treadmill to obstacle to less positive work in strides down from obstacle to treadmill. Stimulation, strain trajectory and their interaction had significant effects on all work loop variables, with the interaction having the largest effect on peak force and work per cycle. These results support the theory that muscle is an active material whose viscoelastic properties are tuned by activation, and which produces forces in response to deformations of length associated with time-varying loads. 

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