Existence, uniqueness and travelling waves to model an invasive specie interaction with heterogeneous reaction and non-linear diffusion

<abstract><p>It is the objective to provide a mathematical treatment of a model to predict the behaviour of an invasive specie proliferating in a domain, but with a certain hostile zone. The behaviour of the invasive is modelled in the frame of a non-linear diffusion (of Porous Medium type) equation with non-Lipschitz and heterogeneous reaction. First of all, the paper examines the existence and uniqueness of solutions together with a comparison principle. Once the regularity principles are shown, the solutions are studied within the Travelling Waves (TW) domain together with stability analysis in the frame of the Geometric Perturbation Theory (GPT). As a remarkable finding, the obtained TW profile follows a potential law in the stable connection that converges to the stationary solution. Such potential law suggests that the pressure induced by the invasive over the hostile area increases over time. Nonetheless, the finite speed, induced by the non-linear diffusion, slows down a possible violent invasion.</p></abstract>

Hall effect on the entropy optimization of radiative magnetized Jeffrey nanofluid flow with homogeneous and heterogeneous reaction by rotating stretching disk

Purpose: The goal of this study is to investigate the entropy optimization of Jeffrey nanofluid flow with the homogeneous and heterogeneous reaction by stretching the rotating disk. The impact of Hall current is also being considered. The process of heat transmission is carried out. For heat transfer coefficient, temperature, concentration, velocity, Bejan number, and entropy generation rate and relevant equations are computed. The implications of various characteristics are investigated. The effect of emerging parameters of nanofluid flow is discussed and represented by a graph. To reduce partial differential equations into ordinary differential equations by using effective similarity transformation. The achieved non-linear system is resolved by the Homotopy analysis technique (HAM) to found the convergent solution of the designated flow problem. The impact of various pertinent parameters, i.e thermal radiations parameter, Brinkman number, Reynolds number, magnetic parameter, Hall Effects parameter, Jeffrey nanofluid parameters are discussed and presented by the graph. Engineering quantities such as Nusselt number and skin friction are also taken into account.

Thermal slip and homogeneous/heterogeneous reaction characteristics of second-grade fluid flow over an exponentially stretching sheet

This paper deals with an unsteady magnetohydrodynamic two-dimensional second-grade fluid flow towards a permeable exponentially stretching surface with heterogeneous–homogeneous reactions. The nonuniform heat source/sink, thermal slip, and thermal radiation effect are also considered to analyze the thermal attributes. The modeled equations of motions are converted into nonlinear ordinary differential equations (ODEs) by suitable transformations. A MATLAB Bvp4c approach is employed for the numerical solution of ODEs. The outcomes of various parameters are scrutinized by graphs. The quantities of interests such as Nusselt number and the skin friction are presented and discussed. The resistance effects take place due to higher estimations of second-grade parameter, as a result, the velocity field declines. The temperature field raises with the increment of radiation parameter. The concentration of nanoparticles decaying when heterogeneous-homogeneous reactions become larger. Moreover, from the tabulated data, it is noticed the growing estimations of K and M boosts the coefficient of skin friction.

Amplified role of potential HONO sources in O₃ formation in North China Plain during autumn haze aggravating processes

Co-occurrences of high concentrations of PM2.5 and ozone (O3) have been frequently observed in haze aggravating processes in the North China Plain (NCP) over the past few years, and higher O3 concentrations during hazy days were supposed to be related to nitrous acid (HONO), but the key sources of HONO enhancing O3 during haze aggravating processes remain unclear, and will be explored in this study by using the WRF-Chem model, which is improved to include ground-based (traffic, soil, and indoor emissions, and the NO2 heterogeneous reaction on ground surface (Hetground)) and aerosol-related (the NO2 heterogeneous reaction on aerosol surfaces (Hetaerosol) and nitrate photolysis (Photnitrate)) potential HONO sources. The results indicate that ground-based HONO sources producing HONO enhancements showed a rapid decrease with height, while the NO+OH reaction and aerosol-related HONO sources decreased slowly with height. Photnitrate contributions to HONO concentrations enhanced with aggravated pollution levels, the enhanced HONO due to Photnitrate in hazy days was about one order of magnitude larger than in clean days and Photnitrate dominated HONO sources (~30–70 % when the ratio of the photolysis frequency of nitrate (Jnitrate) to gas nitric acid (JHNO3) equals 30) at higher layers (> 800 m). Compared with that in clean days, the Photnitrate contribution to the enhanced daily maximum 8-h averaged O3 was increased by over one magnitude during the haze aggravating process. Photnitrate contributed only ~5 % of the surface HONO in daytime with a Jnitrate/JHNO3 ratio of 30 but contributed ~30–50 % of the enhanced O3 near the surface in NCP in hazy days. Surface O3 was dominated by volatile organic compounds-sensitive chemistry, while O3 at higher altitude (> 800 m) was dominated by NOx-sensitive chemistry. Photnitrate had a limited impact on nitrate concentrations (< 15 %) even with a Jnitrate/JHNO3 ratio of 120. The above results suggest that more field studies of Jnitrate in the atmosphere are still needed.

Synergetic effects of NH₃ and NO_<i>x</i> on the production and optical absorption of secondary organic aerosol formation from toluene photooxidation

NH3 is the most important alkaline gas in the atmosphere and one of the key species affecting the behaviors of atmospheric aerosols. However, the impact of NH3 on secondary organic aerosol (SOA) formation remains poorly understood, especially the dynamic evolution of chemical compositions in the SOA formation process. In this study, a series of chamber experiments were performed to probe the individual and common effects of NH3 and NOx on toluene SOA formation through OH photooxidation. The chemical compositions of toluene SOA were characterized using the Aerodyne high-resolution time-of-flight aerosol mass spectrometer (AMS). The SOA yield increased from 28.1 % in the absence of NH3 to 34.7 % in the presence of NH3 but decreased to 19.5 % in the presence of NOx. However, the highest SOA yield of 42.7 % and the lowest carbon oxidation state (OSC) occurred in the presence of both NH3 and NOx, indicating that the higher-volatility products that formed in the presence of NOx could partition into the particle phase when NH3 was added. This resulted in a synergetic effect on SOA formation when NH3 and NOx co-existed. The heterogeneous reaction was the main pathway by which NH3 participated in SOA formation in the photooxidation process. The synergetic effect of NH3 and NOx was also observed in SOA optical absorption. A peak at 280 nm, which is characteristic of organonitrogen imidazole compounds, was observed in the presence of NH3, and its intensity increased when NOx was added into the chamber. This work improves our understanding of how the synergistic interactions between NH3 and NOx influence SOA formation and offers new insights into mitigating haze pollution.

Manganese Dioxide (α-MnO2) and Graphene Oxide (GO) Nanocomposites: An Efficient Promotor for the Oxidative Deprotection of Trimethylsilyl, Tetrahydropyranyl and Methoxymethyl Ethers

Manganese dioxide (α-MnO2) and graphene oxide (GO nanocomposites were prepared and successfully characterized using Fourier-transform infrared (FT-IR), field emission scanning-electron microscopy (FE-SEM), and energy-dispersive X-ray spectroscopy (EDX) mapping methods and Xray diffraction (XRD) analyses. This reagent is an efficient catalyst for the aerobic oxidation of trimethylsilyl (TMS), tetrahedropyranyl (THP), and methoxymethyl ethers (MOM) to their corresponding carbonyl compounds in the presence of K2CO3. All reactions were performed in n-hexane under mild and completely heterogeneous reaction conditions. Our novel method has the advantages of excellent yields, short reaction times, availability and reusability of the catalyst and simple and easy work-up procedure compared to the conventional methods reported in the literature.

Degradation performance and mechanism toward methyl orange via nanoporous copper powders fabricated by dealloying of ZrCuNiAl metallic glassy precursors

The catalyst of nanoporous Cu (NP-Cu) powders, with the chemical composition of Cu79.63Ni6.85O13.53 (at.%), was successfully fabricated by dealloying of Zr-Cu-Ni-Al metallic glassy precursors. The as-prepared NP-Cu powders, co-existing with Cu2O phase on Cu ligament surface, had a three-dimensional (3D) network porous structure. The NP-Cu powders/H2O2 system showed superior catalytic degradation efficiency toward azo dyes in both acidic (pH 2) and neutral (pH 7) environments. Moreover, the cyclic tests indicated that this powder catalyst also exhibited good durability. A novel degradation mechanism of NP-Cu powders/H2O2 was proposed: the high degradation performance in acidic environment was mainly derived from heterogeneous reaction involved with a specific pathway related to Cu3+ to produce HO•, while in neutral environment it was primarily resulted from homogeneous reaction with the generation of HO• from the classical Cu-based Fenton-like process. This work indicates that the NP-Cu powders have great potential applications as catalysts for wastewater treatments.

Physical Aspects of Homogeneous-Heterogeneous Reactions on MHD Williamson Fluid Flow across a Nonlinear Stretching Curved Surface Together with Convective Boundary Conditions

This article is concerned with the fluid mechanics of MHD steady 2D flow of Williamson fluid over a nonlinear stretching curved surface in conjunction with homogeneous-heterogeneous reactions with convective boundary conditions. An effective similarity transformation is considered that switches the nonlinear partial differential equations riveted to ordinary differential equations. The governing nonlinear coupled differential equations are solved by using MATLAB bvp4c code. The physical features of nondimensional Williamson fluid parameter λ , power-law stretching index m , curvature parameter K , Schmidt number Sc , magnetic field parameter M , Prandtl number Pr , homogeneous reaction strength k 1 , heterogeneous reaction strength k 2 , and Biot number γ are presented through the graphs. The tabulated form of results is obtained for the skin friction coefficient. It is noted that both the homogeneous and heterogeneous reaction strengths reduced the concentration profile.