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1. The impact of UV variability on the abundance of bright galaxies at z ≥ 9

   https://doi.org/10.1093/mnras/stad2508  

   Shen, Xuejian; Vogelsberger, Mark; Boylan-Kolchin, Michael; Tacchella, Sandro; Kannan, Rahul (August 2023, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT JWST observations have revealed a population of galaxies bright enough that potentially challenge standard galaxy formation models in the Λ cold dark matter (ΛCDM) cosmology. Using a minimal empirical framework, we investigate the influence of variability on the rest-frame ultra-violet (UV) luminosity function of galaxies at z ≥ 9. Our study differentiates between the median UV radiation yield and the variability of UV luminosities of galaxies at a fixed dark matter halo mass. We primarily focus on the latter effect, which depends on halo assembly and galaxy formation processes and can significantly increase the abundance of UV-bright galaxies due to the upscatter of galaxies in lower-mass haloes. We find that a relatively low level of variability, σUV ≈ 0.75 mag, matches the observational constraints at z ≈ 9. However, increasingly larger σUV is necessary when moving to higher redshifts, reaching $$\sigma _{\rm UV} \approx 2.0\, (2.5)\, {\rm mag}$$ at z ≈ 12 (16). This implied variability is consistent with expectations of physical processes in high-redshift galaxies such as bursty star formation and dust clearance during strong feedback cycles. Photometric constraints from JWST at z ≳ 9 therefore can be reconciled with a standard ΛCDM-based galaxy formation model calibrated at lower redshifts without the need for adjustments to the median UV radiation yield. 

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2. Quantifying Hydrated Electron Transformation Kinetics in UV-Advanced Reduction Processes Using the R _e–,UV Method

   https://doi.org/10.1021/acs.est.2c02003  

   Fennell, Benjamin D.; Odorisio, Adam; McKay, Garrett (July 2022, Environmental Science & Technology)
3. Augmentation of the Photoreactivation Gene in Fremyella diplosiphon Confers UV-B Tolerance

   https://doi.org/10.1021/acsomega.2c03938  

   Gichuki, Samson M.; Arumanayagam, Anithachristy S.; Tabatabai, Behnam; Yalcin, Yavuz S.; Wyatt, LaDonna; Sitther, Viji (September 2022, ACS Omega)
4. Warming and UV Radiation Alleviate the Effect of Virus Infection on the Microalga Emiliania huxleyi

   https://doi.org/10.1111/pce.15262  

   Fu, Qianqian; Huang, Ruiping; Li, Futian; Beardall, John; Hutchins, David A; Liu, Jingwen; Gao, Kunshan (November 2024, Plant, Cell & Environment)

   ABSTRACT The marine microalgaEmiliania huxleyiis widely distributed in the surface oceans and is prone to infection by coccolithoviruses that can terminate its blooms. However, little is known about how global change factors like solar UV radiation (UVR) and ocean warming affect the host‐virus interaction. We grew the microalga at 2 temperature levels with or without the virus in the presence or absence of UVR and investigated the physiological and transcriptional responses. We showed that viral infection noticeably reduced photosynthesis and growth of the alga but was less harmful to its physiology under conditions where UVR influenced viral DNA expression. In the virus‐infected cells, the combination of UVR and warming (+4°C) led to a 13‐fold increase in photosynthetic carbon fixation rate, with warming alone contributing a change of about 5–7‐fold. This was attributed to upregulated expression of genes related to carboxylation and light‐harvesting proteins under the influence of UVR, and to warming‐reduced infectivity. In the absence of UVR, viral infection downregulated the metabolic pathways of photosynthesis and fatty acid degradation. Our results suggest that solar UV exposure in a warming ocean can reduce the severity of viral attack on this ecologically important microalga, potentially prolonging its blooms. 

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5. Elementary reaction-based kinetic model for the fate of N -nitrosodimethylamine under UV oxidation

   https://doi.org/10.1039/D1EW00262G  

   Barrios, Benjamin; Kamath, Divya; Coscarelli, Erica; Minakata, Daisuke (August 2021, Environmental Science: Water Research & Technology)

   null (Ed.)

   UV photolysis is an effective process to remove nitrosamines from contaminated water resources. Nitrosamines represent a class of compounds with high potential for carcinogenicity and, therefore, there are serious concerns regarding their threat to human health and their environmental toxicity. Although the photochemical parameters of parent nitrosamines and their initial reaction pathways are well understood, the fate of nitrogen-containing species and reactive nitrogen species generated from nitrosamine degradation has not yet been elucidated. In this study, we develop an elementary reaction-based kinetic model for the photolysis of N -nitrosodimethylamine (NDMA) and the photochemical transformation products. We use density functional theory quantum mechanical calculations to calculate the aqueous-phase free energies of activation and reaction to investigate the kinetics and thermodynamics properties of the elementary reactions. We generate ordinary differential equations for all species involved in the identified reactions and solve them to obtain the time-dependent concentration profiles of NDMA and the degradation products at pH 3 and pH 7. The profiles are compared to experimental results in the literature to validate our elementary reaction-based kinetic model. This is the first study to develop an elementary reaction-based kinetic model for the photochemical reaction of NDMA and reactive nitrogen species. The findings of this study have a significant impact on the active research area of nitrosative stress and advanced oxidation processes that utilize nitrogen-containing compounds such as UV/nitrate and UV/chloramine advanced oxidation processes. 

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