This paper proposes and analyzes a malaria transmission model structured by the chronological age of the human host population. The model couples an age-structured SIRS system for humans, incorporating waning immunity, with an SI system for mosquitoes under mass-action transmissions. Using integrated semigroup theory and spectral analysis, we establish the well-posedness of the model, derive the basic reproduction number, and prove the global asymptotic stability of the parasite-free equilibrium by using a Lyapunov functional when R0≤1, thereby excluding the possibility of backward bifurcation. Numerical simulations suggest the global stability of the endemic equilibrium when R0>1, while the analytical proof remains an open problem.
Given the significant climatic role of sulfuric acid (SA) and methanesulfonic acid (MSA), this work examines the hydration-driven formation of ternary MSA(SA)(W)n=1–10 clusters via DFT (M06-2X, X3LYP, APF-D, PW6B95 combined with Def2-TZVP). We report structures, Boltzmann populations, binding energies and binding free energies (ΔE, ΔG), and binding energies per-water moleculs (ΔE/W, ΔG/W). While clusters of size n = 7–10 are inherently stable, their atmospheric equilibrium concentrations are low. The MSA(SA)(W)4 cluster is an exception, with a concentration of 10³ molecules/cm³ and a low evaporation rate. Clusters of size n = 4,7,8 exhibit slow evaporation ( < 10⁵ s⁻¹), suggesting extended atmospheric lifetimes. All DFT methods yield consistent trends, with M06-2X closest to PW91/6-311 + + G(3df,3pd) reference values. Cluster concentrations are sensitive to relative humidity (20, 50, and 100
This work examines low-frequency ion-acoustic solitary structures in a weakly rotating, magnetized, collisional electron-positron-ion plasma. In this model, the electrons and positrons obey a q -nonextensive distribution, while ions are treated as a warm fluid subject to ion-neutral collisions and an externally applied periodic force. By employing the reductive perturbation technique, the governing fluid and Poisson equations are reduced to a forced damped Zakharov-Kuznetsov (FDZK) equation that consistently incorporates four key physical ingredients in a unified framework: nonextensive statistics, collisional dissipation, Coriolis effects due to plasma rotation, and external energy injection through a periodic source term. In the collisionless, force-free limit, an exact compressive solitary wave solution of the underlying Zakharov–Kuznetsov equation is obtained, and the corresponding pseudo-potential analysis clarifies the constraints on the existence region of ion-acoustic solitary waves and their polarity. For weak damping and finite periodic forcing, approximate time-dependent solitary solutions of the FDZK equation are constructed using energy-type conservation arguments, allowing the combined impact of dissipation and external driving on the soliton profile (amplitude, width, and speed) to be quantified. The impact of various related parameters on the dissipative soliton profiles is numerically investigated. These findings offer a physically transparent picture of how nonthermal statistics, rotation, and external excitations jointly shape nonlinear ion-acoustic dynamics in realistic space and laboratory plasmas, such as planetary and pulsar magnetospheres, the solar wind, and magnetized laboratory devices.
Industrial effluents from metallurgy, chemicals, and other sectors are major releasers of heavy metals polluting the environment. Within this study, chitosan (CS) and nanocellulose (NCs) were extracted from fish scales and coconut fiber, respectively, and co-precipitated in sodium alginate (ALG) solution to produce a biocomposite hydrogel (CS@NCs/ALG). The adsorptive efficiency of the new composite was determined for detoxification of 2 heavy metals (Hg2+, Zn2+) from aqueous solution. The main physicochemical properties of CS@NCs/ALG were characterized by application of spectroscopy (FTIR, XRD, SEM-EDX), with analytical methods including BET, TGA, pHPZC. The results show that CS@NCs/ALG exhibits a heterogenous and mesoporous structure with surface functional groups including -OH, -NH2, and -COOH groups. Removal tests indicated that the adsorption of these metals was strongly influenced by solution pH. Modelling of the adsorption results indicated best fits to the pseudo-second order kinetic and Langmuir isotherm models. High adsorption capacities (402.89 and 500.48 mg g− 1) were obtained for Hg2+ and Zn2+. Thermodynamic analysis revealed that the adsorption of both ions was thermodynamically favorable, spontaneous, and accompanied by decreased randomness. These findings demonstrate that the hydrogel composite has high adsorption potential and can be effectively applied for bivalent heavy metal detoxification from contaminated aquatic systems.
The electronic structure and spectroscopic properties of dihydrodehydrodiconiferyl-9-O-sulfate alcohol (DDDC-9-OS), a phenolic neolignan sulfate in methanolic solution were investigated using density functional theory (DFT). An extensive benchmark of functionals, including B3LYP, B3LYP-D3BJ, PW6B95, PW6B95D, omega B97X-D, MPWPKZB, and LC-TPSSTPSS, combined with the 6-311++G(d,p) and cc-pVTZ basis sets, was performed to simulate nuclear magnetic resonance (NMR) chemical shifts and vibrational (IR and Raman) spectra. With mean variances less than 4%, the calculated harmonic frequencies showed excellent agreement with experimental infrared data. While the B3LYP/6-311++G(d,p) level theory offered the closest match to experimental IR band intensities, chemical shift predictions from the CSGT/omega B97X-D/6-311++G(d,p) method shown good agreement with experimental NMR values. The intramolecular charge distribution, reactivity, and non-covalent interactions controlling the stability of the molecule were also profoundly revealed by a thorough examination of the electronic structure using the B3LYP-D3BJ/6-311++G(d,p) level, which included the electron localization function (ELF), frontier molecular orbitals (FMO), reduced density gradient non-covalent interactions (RDG-NCI), and molecular electrostatic potential (MEP).
