Landfill gas (LFG) is a renewable yet highly diluted fuel whose variable composition and operation at elevated pressures pose significant challenges for stable and efficient combustion. In this work, the laminar burning velocity (LBV) and Markstein length of realistic CH4-CO2-N2 mixtures were investigated experimentally and numerically at 298 K, at pressures up to 5 bar, and for equivalence ratios ranging from 0.6 to 1.3, with special focus on the lean region where new burners concepts are expected operate and where data is quite scarce. Two surrogate fuels containing 65% and 55% CH4 were formulated while maintaining a constant CO2:N2 ratio to isolate the effect of total dilution. Experimental LBVs were determined using the outwardly propagating spherical flame method and compared with detailed chemical-kinetic mechanisms. Among the mechanisms evaluated, Konnov Mech 0.6 provided the best agreement with experimental data at 1 bar. The results show that increasing pressure and dilution both significantly reduce the LBV; however, they act through distinct mechanisms. Dilution primarily suppresses flame propagation through thermal effects, reducing adiabatic flame temperature and overall reaction rates, whereas pressure enhances competition between chain-branching and termination reactions, leading to reduced radical concentrations. Sensitivity and pathway analyses identified the reaction H + O2 -><- O + OH as the dominant promoting step controlling flame propagation under all conditions. The Markstein length was found to increase from lean to rich mixtures and to decrease with increasing pressure, indicating enhanced flame instability at elevated pressures. The present study provides new high-pressure experimental data and a detailed mechanistic interpretation of LFG combustion, contributing to improved modeling and the design of energy systems operating with low-calorific-value fuels.
In this paper, we perform a classification of Lie point symmetries of a (3+1)-dimensional model describing tumour cells, extracellular matrix (ECM), and matrix-degrading enzymes (MDEs). From the symmetries, we were able to find new exact solutions for the model. One of the solutions we found has haptotaxis effect. We explore these solutions, analysing the invasion of tumour cells, the evolution of the ECM degradation by MDEs and the diffusion of the MDEs. We also obtain three conserved currents and from them we explore the time variation of certain biological quantities.
In this manuscript, we prove the existence of strictly positive solutions for a class of p&q systems whose nonlinearities involved may exhibit semipositone behavior, which arise naturally in several applications that includes models of competing species and the dynamics of particle movement. Our approach combines variational methods, comparison principles and a novel regularity result for systems. This estimate, which may be of independent interest, is new even in the classical Laplacian case.
Anthropogenic land-use change drives biodiversity loss by altering habitat structure, reducing connectivity, and reshaping ecological processes, even within protected areas. Although protected areas are key for biodiversity conservation, their effectiveness may depend on the surrounding landscape context. This study evaluates the effects of land use around and within protected areas on species richness and functional diversity in amphibian assemblage. Data were collected during 12 monthly expeditions between January 2013 and December 2014, sampling 81 ponds across eight protected areas and surrounding landscapes in southern Brazil. We measured species richness, abundance, and 21 ecomorphological traits, using phylogenetic eigenvector regression to control phylogenetic autocorrelation. Functional diversity was estimated as the total branch length of functional dendrograms. Structural equation modelling was used to assess the effects of spatial, landscape, land use, and habitat variables on species richness, abundance, and functional diversity. Land use, hydroperiod, and spatial configuration shaped amphibian assemblages through different mechanisms. Species richness was mainly driven by vegetation heterogeneity in ponds, abundance and pond connectivity, whereas functional diversity responded to land use, native landscape and hydroperiod. Anthropogenic land use (e.g., agriculture and reforestation) was positively associated with functional diversity, likely reflecting shifts toward generalist and disturbance-tolerant species rather than improved environmental conditions. Overall, our results show that different diversity dimensions respond to distinct drivers, and that land-use change can reorganize functional structure. We highlight the importance of conserving interconnected ponds with diverse hydroperiods and high vegetation heterogeneity within and around protected areas to maintain amphibian diversity and avoid long-term functional homogenization.
This study presents a comprehensive chemical characterization of the Antarctic endemic brown macroalga Desmarestia menziesii, collected from Penguin and Livingston Islands (Antarctic Peninsula). Sequential extraction with solvents of increasing polarity (hexane, dichloromethane, ethyl acetate, and methanol) was performed on 601.43 g of lyophilized biomass, followed by GC–MS, NMR, IR, and mass spectrometry analyses. The apolar extracts revealed a complex lipophilic profile including marine sterols (fucosterol, isofucosterol, 24-ethylcholesta-5,24(25)-dienol, and stigmasta-5,24(28)-dien-3-ol), saturated and unsaturated fatty acids, phenolic derivatives, and rare long-chain hydrocarbons (> C23). These metabolites are associated with membrane stabilization, homeoviscous adaptation, and oxidative stress mitigation under chronic low temperatures and high UV radiation typical of Antarctic environments. The ethyl acetate extract contained UV-fluorescent aromatic meroterpenoids with confirmed antioxidant activity via TLC-DPPH bioautography, reinforcing their ecological role in photoprotection. The methanolic extract was predominantly composed of mannitol (52.5
