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.

Meeting the anticipated 50% increase in global food demand by 2050 requires a crucial reassessment of agricultural practices, particularly in terms of nitrogen fertilizers inputs. This study analyzes the technical potential of nitrogen recovery from livestock manure and crop residues, bringing attention to the often-overlooked resource of digestate derived from anaerobic digestion. Our analysis highlights the significant capacity of the anaerobic digestion process, yielding approximately 234 +/- 5 million metric tons (Mt) of nitrogen annually, sourced 93% from livestock manure and 7% from crop residues. Additionally, we estimated that substituting synthetic nitrogen with nitrogen from anaerobic digestion has the potential to reduce greenhouse gas emissions by 70% (185 Mt CO2-eq yr-1). Lastly, 2.5 billion people could be sustained by crops grown using nitrogen from anaerobic digestion of manure and crop residues rather than synthetic nitrogen fertilizers. Although agricultural residues have double the technical potential of current synthetic nitrogen fertilizer production, 30% of croplands encounter difficulties in satisfying their nitrogen needs solely through crop residues and anaerobic digestion manure. This deficiency primarily results from inefficient reuse attributed to geographical mismatches between crop and livestock systems. This underscores the urgent need to reconnect livestock and cropping systems and facilitate the transport and reuse of manure in crop production. In conclusion, the mobilization of these large amounts of nitrogen from livestock manure and crop residues will require to overcome the nitrogen from anaerobic digestion green premium with incentives and subsidies.

The current centralized configuration of the ammonia industry makes the production of nitrogen fertilizers susceptible to the volatility of fossil fuel prices and involves complex supply chains with long-distance transport costs. An alternative consists of on-site decentralized ammonia production using small modular technologies, such as electric Haber-Bosch or electrocatalytic reduction. Here we evaluate the cost-competitiveness of producing low-carbon ammonia at the farm scale, from a solar agrivoltaic system, or using electricity from the grid, within a novel global fertilizer industry. Projected costs for decentralized ammonia production are compared with historical market prices from centralized production. We find that the cost-competitiveness of decentralized production relies on transport costs and supply chain disruptions. Taking both factors into account, decentralized production could achieve cost-competitiveness for up to 96% of the global ammonia demand by 2030. These results show the potential of decentralized ammonia technologies in revolutionizing the fertilizer industry, particularly in regions facing food insecurity.

Perturbations to stellar systems can reflect the gravitational influence of dark matter substructures. On scales much smaller than the size of a stellar system, we point out analytical connections between the stellar and dark matter distributions. In particular, the density and velocity power spectra of the stars are proportional to the density power spectrum of the perturbing dark matter, scaled by k(-4). This relationship allows easy evaluation of the suitability of a stellar system for detecting dark substructure. As examples, we show that the Galactic stellar halo is expected to be sensitive to cold dark matter substructure at wavenumbers k less than or similar to 0.3 kpc(-1), and the Galactic disc might be sensitive to substructure at wavenumbers k similar to 4 kpc(-1). The perturbations considered in this work are short-lived, being rapidly erased by the stellar velocity dispersion, so it may be possible to attribute a detection to dark matter substructure without ambiguity.

In cosmologies with an early matter -dominated era (EMDE) prior to Big Bang nucleosynthesis, the boosted growth of small-scale matter perturbations during the EMDE leads to microhalo formation long before halos would otherwise begin to form. For a range of models, halos can even form during the EMDE itself. These halos would dissipate at the end of the EMDE, releasing their gravitationally heated dark matter and thereby imprinting a free -streaming cut-off on the matter power spectrum. We conduct the first cosmological N -body simulations of the formation and evaporation of halos during and after an EMDE. We show that in these scenarios, the free -streaming cut-off after the EMDE can be predicted accurately from the linear matter power spectrum. Although the free streaming can erase much of the EMDE-driven boost to density perturbations, we use our findings to show that the (re -)formation of halos after the EMDE nevertheless proceeds before redshift similar to 1000. Early -forming microhalos are a key observational signature of an EMDE, and our prescription for the impact of gravitational heating will allow studies of the observational status and prospects of EMDE scenarios to cover a much wider range of parameters.

We present stellar age determinations for 4661 red giant branch stars in the APO-K2 catalog, derived using mass estimates from K2 asteroseismology from the K2 Galactic Archaeology Program and elemental abundances from the Apache Point Galactic Evolution Experiment survey. Our sample includes 17 of the 19 fields observed by K2, making it one of the most comprehensive catalogs of accurate stellar ages across the Galaxy in terms of the wide range of populations spanned by its stars, enabling rigorous tests of Galactic chemical evolution models. Taking into account the selection functions of the K2 sample, the data appear to support the age-chemistry morphology of stellar populations predicted by both inside-out and late-burst scenarios. We also investigate trends in age versus stellar chemistry and Galactic position, which are consistent with previous findings. Comparisons against APOKASC-3 asteroseismic ages show agreement to within similar to 3%. We also discuss offsets between our ages and spectroscopic ages. Finally, we note that ignoring the effects of alpha-enhancement on stellar opacity (either directly or with the Salaris metallicity correction) results in an similar to 10% offset in age estimates for the most alpha-enhanced stars, which is an important consideration for continued tests of Galactic models with this and other asteroseismic age samples.

The surface [C/N] ratios of evolved giants are strongly affected by the first dredge-up (FDU) of nuclear-processed material from stellar cores. C and N also have distinct nucleosynthetic origins and serve as diagnostics of mixing and mass-loss. We use subgiants to find strong trends in the birth [C/N] with [Fe/H], which differ between the low-alpha and high-alpha populations. We demonstrate that these birth trends have a strong impact on the surface abundances after the FDU. This effect is neglected in current stellar models, which use solar-scaled C and N. We map out the FDU as a function of evolutionary state, mass, and composition using a large and precisely measured asteroseismic data set in first-ascent red giant branch (RGB) and core He-burning, or red clump (RC), stars. We describe the domains where [C/N] is a useful mass diagnostic and find that the RC complements the RGB and extends the range of validity to higher mass. We find evidence for extra mixing on the RGB below [Fe/H] = -0.4, matching literature results, for high-alpha giants, but there is no clear evidence of mixing in the low-alpha giants. The predicted signal of mass-loss is weak and difficult to detect in our sample. We discuss implications for stellar physics and stellar population applications.

Cobalt pollution is harmful to both the aquatic ecosystem and human health. As the primary producer of aquatic ecosystems in hypersaline environments, unicellular planktonic Dunaliella microalgae is considered to be a low-energy and eco-friendly biosorbent that removes excess cobalt and enhances the vitality of coastal and marine ecosystems. In this study, we found that the halotolerant microalga named Dunaliella sp. FACHB-558 could grow under a salinity condition with 0.5-4.5M NaCl. A phylogenetic analysis based on the rbcL gene revealed that Dunaliella sp. FACHB-558 is a close relative of Dunaliella primolecta TS-3. At lab-scale culture, Dunaliella sp. FACHB-558 exhibited high tolerance to heavy metal stresses, including cobalt, nickel, and cadmium. Treatment with 60muM cobalt delayed its stationary phase but ultimately led to a higher population density. Furthermore, Dunaliella sp. FACHB-558 has the ability to adsorb the cobalt ions in the aquatic environment, which was evidenced by the decreased amount of cobalt in the culture medium. In addition, the tolerance of Dunaliella sp. FACHB-558 to cobalt stress was correlated with enhanced nitric oxide content and peroxidase activity. The autophagy inhibitor 3-MA enhanced nitric oxide burst, increased peroxidase activity, and accelerated the bioremoval of cobalt, suggesting that the autophagy pathway played a negative role in response to cobalt stress in Dunaliella sp. FACHB-558. In summary, our study identified a novel microalga possessing high cobalt tolerance and provided a promising natural biosorbent for the research and application of heavy metal bioremediation technology.

We report the discovery of large, ionized, [O ii]-emitting circumgalactic nebulae around the majority of 30 UV-luminous quasars at z = 0.4-1.4 observed with deep, wide-field integral field spectroscopy with the Multi-Unit Spectroscopy Explorer (MUSE) by the Cosmic Ultraviolet Baryon Survey and MUSE Quasar Blind Emitters Survey. Among the 30 quasars, seven (23%) exhibit [O ii]-emitting nebulae with major axis sizes greater than 100 kpc, 20 greater than 50 kpc (67%), and 27 (90%) greater than 20 kpc. Such large, optically emitting nebulae indicate that cool, dense, and metal-enriched circumgalactic gas is common in the halos of luminous quasars at intermediate redshift. Several of the largest nebulae exhibit morphologies that suggest interaction-related origins. We detect no correlation between the sizes and cosmological-dimming-corrected surface brightnesses of the nebulae and quasar redshift, luminosity, black hole mass, or radio-loudness, but find a tentative correlation between the nebulae and rest-frame [O ii] equivalent width in the quasar spectra. This potential trend suggests a relationship between interstellar medium content and gas reservoirs on CGM scales. The [O ii]-emitting nebulae around the z approximate to 1 quasars are smaller and less common than Ly alpha nebulae around z approximate to 3 quasars. These smaller sizes can be explained if the outer regions of the Ly alpha halos arise from scattering in more neutral gas, by evolution in the cool circumgalactic medium content of quasar-host halos, by lower-than-expected metallicities on greater than or similar to 50 kpc scales around z approximate to 1 quasars, or by changes in quasar episodic lifetimes between z = 3 and 1.