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This paper systematically evaluates how, and to what extent, nanosecond repetitively pulsed (NRP) discharges modify the laminar flame speed of methane–air mixtures at ambient conditions, using both experiments in a narrow-channel quartz burner and a one-dimensional plasma-combustion model described in an accompanying paper (Part I). By varying the discharge location relative to the flame, four actuation strategies were explored at variable pulse repetition frequency: (i) discharges far ahead of the flame, (ii) pre-treatment of fresh reactants, (iii) direct (insitu) plasma–flame overlap, and (iv) a combination of pre-treatment and insitu interaction. Results show that acoustic waves produced by upstream discharges can reduce flame speed by as much as 30%–40%; while partially overlapping the discharge with the flame significantly accelerates it, with measured enhancements of up to 50% in both model and experiment. Flame speed modification by plasma increased with pulse repetition frequency, so that the envelope of performance enhancement reported here is limited by the highest frequencies tested (8kHz). The model captures these trends by attributing the detrimental effects to pressure-wave disturbances and the beneficial effects to radical-seeding and mild heat addition in, and close to, the reaction zone. These observations may help shed light on previously reported experiments and are here presented in a unified manner by focusing on a fundamental combustion metric (laminar flame speed), to give generality to the results obtained in laminar flames. The results demonstrate how spatio-temporal positioning of the discharge governs whether plasma aids or hinders the flame, ultimately guiding the design of optimal plasma-assisted combustion strategies. 

Plasma-assisted combustion (PAC) offers significant potential to enhance combustion processes by modifying thermal, kinetic, and transport properties. Despite progress in the field, challenges remain in reconciling disparate experimental results and understanding the mechanisms of plasma-flame interaction. This work develops a numerical modeling framework to systematically evaluate the impact of Nanosecond Repetitively Pulsed Discharges (NRPDs) on PAC systems. The focus of this contribution is modeling laminar premixed flames; and the main metric to assess the impact of plasma on flame is the laminar flame speed. The model is exercised on a stoichiometric methane/air flame. A combined 0D plasma-combustion model, PlasmaChem, is presented, enabling accurate energy tracking and coupling of detailed plasma and combustion mechanisms. The model is extended to 1D to incorporate compressible fluid dynamics, capturing the interaction between plasma and flame propagation. The results reveal distinct phases of plasma-flame interaction, demonstrating both beneficial effects, such as increased laminar flame speed due to radical production, and adverse effects, including flame deceleration from pressure disturbances. The model is compared to experiments in an accompanying paper, Part II of this work. 

Abstract BackgroundAs habitat fragmentation increases, ecological processes, including patterns of vector-borne pathogen prevalence, will likely be disrupted, but ongoing investigations are necessary to examine this relationship. Here, we report the differences in the prevalence of Lyme disease (Borrelia burgdorferisensu lato, s.l.) and haemoproteosis (Haemoproteusspp.) pathogens in avian populations of a fragmented habitat.B. burgdorferis.l. is a generalist pathogen that is transmitted byIxodes pacificusvectors in California, andHaemoproteusis an avian parasite transmitted byCulicoidesvectors. MethodsTo determine whether biotic (avian and mammalian abundance) or abiotic characteristics (patch size and water availability) correlated with infection prevalence change, we screened 176 birds sampled across seven sites in oak woodland habitat in northern California. ResultsWhile biotic factors correlated with an increase in both pathogens, infection prevalence ofHaemoproteusspp. was only associated with individual-level traits, specifically foraging substrate and diet, andB. burgdorferis.l. was associated with community-level characteristics, both total mammal and, specifically, rodent abundance. Proximity to water was the only abiotic factor found to be significant for both pathogens and reinforces the importance of water availability for transmission cycles. Larger patch sizes did not significantly affect infection prevalence ofHaemoproteus,but did increase the prevalence ofB. burgdorferi. ConclusionsThese results highlight that while environmental factors (specifically habitat fragmentation) have a limited role in vector-borne pathogen prevalence, the indirect impact to biotic factors (community composition) can have consequences for bothHaemoproteusandB. burgdorferiprevalence in birds. Given the pervasiveness of habitat fragmentation, our results are of broad significance. Graphical abstract 

ABSTRACT Neuromesodermal progenitors (NMPs) are a vertebrate cell type that contribute descendants to both the spinal cord and the mesoderm. The undifferentiated bipotential NMP state is maintained when both Wnt signaling is active and Sox2 is present. We used transgenic zebrafish reporter lines to live-image both Wnt activity and Sox2 levels in NMPs and observed a unique cellular ratio in NMPs compared to NMP-derived mesoderm or neural tissue. We used this unique signature to identify the previously unknown anatomical position of a progenitor population that gives rise to midline tissues of the floor plate of the spinal cord and the mesodermal notochord. Thus, quantification of the active Wnt signaling to Sox2 ratio can be used to predict and identify cells with neuromesodermal potential. We also developed the auxin-inducible 2 degron system for use in zebrafish to test the temporal role that Sox2 plays during midline formation. We found that ectopic Sox2 in the presence of Wnt activity holds cells in the undifferentiated floor plate/notochord progenitor state, and that degradation of the ectopic Sox2 is required for cells to adopt a notochord fate.