Microalgae contribute to about half of global net photosynthesis, which converts sunlight into the chemical energy (ATP and NADPH) used to transform CO2 into biomass. Alternative electron pathways of photosynthesis have been proposed to generate additional ATP that is required to sustain CO2 fixation. However, the relative importance of each alternative pathway remains elusive. Here, we dissect and quantify the contribution of cyclic, pseudo-cyclic and chloroplast-to-mitochondria electron flows for their ability to sustain net photosynthesis in the microalga Chlamydomonas reinhardtii. We show that (i) each alternative pathway can provide sufficient additional energy to sustain high CO2 fixation rates, (ii) the alternative pathways exhibit cross-compensation, and (iii) the activity of at least one of the three alternative pathways is necessary to sustain photosynthesis. We further show that all pathways have very different efficiencies at energizing CO2 fixation, with the chloroplast-mitochondria interaction being the most efficient. Overall, our data lay bioenergetic foundations for biotechnological strategies to improve CO2 capture and fixation.

The thylakoid membrane lipid sulfoquinovosyldiacylglycerol (SQDG) is an anionic molecule that functions in stabilizing the thylakoid membranes and photosystem (PS) supercomplexes. In this study, we characterized the function of GreenCut protein CrLPB1, which encodes UDP-glucose pyrophosphorylase (UGP3), an enzyme involved in SQDG biosynthesis. The lpb1 mutants had reduced levels of SQDG, grew more slowly than wild type cells or the complemented strain under photoautotrophic conditions and were impacted in its rate of oxygen evolution and photosystem II (PSII) activity, especially electron transfer from Q(A)(-) to Q(B). Furthermore, the structure of the PSII supercomplex and morphology of the thylakoid membranes were also both altered in lpb1. In conclusion, LPB1 is involved in SQDG biosynthesis, which in turn appears to be critical in maintaining normal thylakoid membrane structure and PSII activity/stability.

Simple models have been used to describe ecological processes for over a century. However, the complexity of ecological systems makes simple models subject to modelling bias due to simplifying assumptions or unaccounted factors, limiting their predictive power. Neural ordinary differential equations (NODEs) have surged as a machine-learning algorithm that preserves the dynamic nature of the data (Chen et al. 2018 Adv. Neural Inf. Process. Syst.). Although preserving the dynamics in the data is an advantage, the question of how NODEs perform as a forecasting tool of ecological communities is unanswered. Here, we explore this question using simulated time series of competing species in a time-varying environment. We find that NODEs provide more precise forecasts than autoregressive integrated moving average (ARIMA) models. We also find that untuned NODEs have a similar forecasting accuracy to untuned long-short term memory neural networks and both are outperformed in accuracy and precision by empirical dynamical modelling . However, we also find NODEs generally outperform all other methods when evaluating with the interval score, which evaluates precision and accuracy in terms of prediction intervals rather than pointwise accuracy. We also discuss ways to improve the forecasting performance of NODEs. The power of a forecasting tool such as NODEs is that it can provide insights into population dynamics and should thus broaden the approaches to studying time series of ecological communities.

We have conducted a systematic search around the Milky Way (MW) analog NGC 253 (D = 3.5 Mpc), as a part of the Panoramic Imaging Survey of Centaurus and Sculptor (PISCeS)-a Magellan+Megacam survey to identify dwarfs and other substructures in resolved stellar light around MW-mass galaxies outside of the Local Group. In total, NGC 253 has five satellites identified by PISCeS within 100 kpc with an absolute V-band magnitude of M-V < -7. We have additionally obtained deep Hubble Space Telescope imaging of four reported candidates beyond the survey footprint: Do III, Do IV, and dw0036m2828 are confirmed to be satellites of NGC 253, while SculptorSR is found to be a background galaxy. We find no convincing evidence for the presence of a plane of satellites surrounding NGC 253. We construct its satellite luminosity function, which is complete down to M-V less than or similar to -8 out to 100 kpc and M-V less than or similar to -9 out to 300 kpc, and compare it to those calculated for other Local Volume galaxies. Exploring trends in satellite counts and star-forming fractions among satellite systems, we find relationships with host stellar mass, environment, and morphology, pointing to a complex picture of satellite formation, and a successful model has to reproduce all of these trends.

We present the first detailed chemical-abundance analysis of stars from the dwarf-galaxy stellar stream Wukong/LMS-1 covering a wide metallicity range (-3.5 < [Fe/H] less than or similar to -1.3). We find abundance patterns that are effectively indistinguishable from the bulk of Indus and Jhelum, a pair of smaller stellar streams proposed to be dynamically associated with Wukong/LMS-1. We confirmed a carbon-enhanced metal-poor star ([C/Fe] > +0.7 and [Fe/H] similar to -2.9) in Wukong/LMS-1 with strong enhancements in Sr, Y, and Zr, which is peculiar given its solar-level [Ba/Fe]. Wukong/LMS-1 stars have high abundances of alpha elements up to [Fe/H] greater than or similar to -2$, which is expected for relatively massive dwarfs. Towards the high-metallicity end, Wukong/LMS-1 becomes alpha-poor, revealing that it probably experienced fairly standard chemical evolution. We identified a pair of N- and Na-rich stars in Wukong/LMS-1, reminiscent of multiple stellar populations in globular clusters. This indicates that this dwarf galaxy contained at least one globular cluster that was completely disrupted in addition to two intact ones previously known to be associated with Wukong/LMS-1, which is possibly connected to similar evidence found in Indus. From these >= 3 globular clusters, we estimate the total mass of Wukong/LMS-1 to be approximate to 10(10)M(circle dot), representing similar to 1 per cent of the present-day Milky Way. Finally, the [Eu/Mg] ratio in Wukong/LMS-1 continuously increases with metallicity, making this the first example of a dwarf galaxy where the production of r-process elements is clearly dominated by delayed sources, presumably neutron-star mergers.

Decades of measurements of the thermophysical properties of hot metals show that pulsed Joule heating is an effective method to heat solid and liquid metals that are chemically reactive or difficult to contain. To extend such measurements to hundreds of GPa pressure, pulsed heating methods have recently been integrated with diamond anvil cells. The recent design used a low-side switch and active electrical sensing equipment that was prone to damage and measurement error. Here, we report the design and characterization of new electronics that use a high-side switch and robust, passive electrical sensing equipment. The new pulse amplifier can heat 5 to 50 mum diameter metal wires to thousands of kelvin at tens to hundreds of GPa using diamond anvil cells. Pulse durations and peak currents can each be varied over three orders of magnitude, from 5 s to 10ms and from 0.2 to 200A. The pulse amplifier is integrated with a current probe. Two voltage probes attached to the body of a diamond anvil cell are used to measure voltage in a four-point probe geometry. The accuracy of four-point probe resistance measurements for a dummy sample with 0.1 Omega resistance is typically better than 5% at all times from 2 s to 10ms after the beginning of the pulse.

We present the initial sample of redshifts for 3839 galaxies in the MeerKAT DEEP2 field-the most sensitive similar to 1.4 GHz radio field yet observed with sigma(n) = 0.55 mu Jy beam(-1), reaching the confusion limit. Using a spectrophotometric technique combining coarse optical spectra with broadband photometry, we obtain redshifts with sigma(z )less than or similar to 0.01(1 + z), as determined from repeat observations. The resulting radio luminosity functions between 0.2 < z < 1.3 from our sample of 3839 individual galaxies are in remarkable agreement with those inferred from previous modeling of radio source counts, confirming a greater than or similar to 50% excess in radio-based star formation rate density (SFRD) (z) measurements at 0.2 < z < 1.3 compared to those from the UV-IR. Several sources of systematic error are discussed-totalling similar to 0.13 dex when added in quadrature. Even in the event that all systematic errors work to decrease the radio-based SFRD values, they are incapable of reconciling differences between the radio-based measurements with those from the UV-IR at 0.5 < z < 1.3. We conclude that significant work remains to have confidence in a full accounting of the star formation budget of the Universe.

H ii region electron temperatures are a critical ingredient in metallicity determinations, and recent observations have revealed systematic variations in the temperatures measured using different ions. We present electron temperatures (T-e) measured using the optical auroral lines ([N ii]lambda 5756, [O ii]lambda lambda 7320, 7330, [S ii]lambda lambda 4069, 4076, [O iii]lambda 4363, and [S iii]lambda 6312) for a sample of H ii regions in seven nearby galaxies. We use observations from the Physics at High Angular resolution in Nearby Galaxies survey (PHANGS) obtained with integral field spectrographs on Keck (Keck Cosmic Web Imager) and the Very Large Telescope (Multi-Unit Spectroscopic Explorer). We compare the different T-e measurements with H ii region and ISM environmental properties such as electron density, ionization parameter, molecular gas velocity dispersion, and stellar association/cluster mass and age obtained from PHANGS. We find that the temperatures from [O ii] and [S ii] are likely overestimated due to the presence of electron density inhomogeneities in H ii regions. We measure high [O iii] temperatures in a subset of regions with high molecular gas velocity dispersion and low ionization parameter, which may be explained by the presence of low-velocity shocks. In agreement with previous studies, the T-e-T-e between [N ii] and [S iii] temperatures have the lowest observed scatter and follow predictions from photoionization modeling, which suggests that these tracers reflect H ii region temperatures across the various ionization zones better than [O ii], [S ii], and [O iii].

The European ammonia industry emits 36 million tons of carbon dioxide annually, primarily from steam methane reforming (SMR) hydrogen production. These emissions can be mitigated by producing hydrogen via water electrolysis using dedicated renewables with grid backup. This study investigates the impact of decarbonization targets for hydrogen synthesis on the economic viability and technical feasibility of retrofitting existing European ammonia plants for on-site, semi-islanded electrolytic hydrogen production. Results show that electrolytic hydrogen cuts emissions, on average, by 85% (36%-100% based on grid price and carbon intensity), even without enforcing emission limits. However, an optimal lifespan average well-to-gate emission cap of 1 kg carbon dioxide equivalent (CO2e)/kg H2 leads to a 95% reduction (92%-100%) while maintaining cost-competitiveness with SMR in renewable-rich regions (mean levelized cost of hydrogen (LCOH) of 4.1 euro/kg H2). Conversely, a 100% emissions reduction target dramatically increases costs (mean LCOH: 6.3 euro/kg H2) and land area for renewables installations, likely hindering the transition to electrolytic hydrogen in regions with poor renewables and limited land. Increasing plant flexibility effectively reduces costs, particularly in off-grid plants (mean reduction: 32%). This work guides policymakers in defining cost-effective decarbonization targets and identifying region-based strategies to support an electrolytic hydrogen-fed ammonia industry.