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Interfacial reactions between iron (Fe) (hydr)oxide surfaces and the activity of bacteria during dissimilatory Fe reduction affect extracellular electron transfer. The presence of organic matter (OM) and exposed facets of Fe (hydr)oxides influence this process. However, the underlying interfacial mechanism of facet-dependent hematite and its toxicity toward microbes during bioreduction in the presence of OM remains unknown. Herein, humic acid (HA), as typical OM, was selected to investigate its effect on the bioreduction of hematite {100} and {001}. When HA concentration was increased from 0 to 500 mg L

Iron (Fe) oxides and fulvic acid (FA) are the key components affecting the fate of cadmium (Cd) in soil. The presence of FA influences Fe mineral transformation, and FA may complicate phase transformation and dynamic behavior of Cd. How varying Fe minerals and FA affect Cd immobilization during the ferrihydrite transformation induced by various Fe(II) concentrations, however, is still lack of quantitative understanding. In this study, we built a model for Cd species quantification during phase transformation based on mechanistic insights obtained from batch experiments. Spectroscopic analysis showed that Fe(II) concentrations affected secondary Fe minerals formation under the condition of co-existence of Cd and FA, and ultimately changed the distribution of Cd and FA. Microscopic analysis revealed that besides surface adsorption, part of Cd was sequestrated by magnetite, whereas FA was able to diffuse into lepidocrocite defects. The model revealed that adsorbed Cd was mainly controlled by FA and ferrihydrite, and direct complexation of Cd by FA had a strong impact on the continuous change in Cd at lower Fe(II) concentration. The results contribute to an in-depth understanding of the mobility of Cd in the environment and provide a method for quantifying the dynamic behavior of heavy metals in multi-reactant systems.

In this paper, we consider a HIV infection model with CTL-response delay and analyze the effect of time delay on stability of equilibria. We obtain the global stability of the infection-free equilibrium and give sufficient conditions for the local stability of the CTL-absent equilibrium and CTL-present equilibrium. By choosing the CTL-response delay τ as a bifurcation parameter, we prove that the CTL-present equilibrium is locally asymptotically stable in a range of delays and a Hopf bifurcation occurs as τ crosses a critical value. Numerical simulations are given to support the theoretical results.

In this paper, we revisit Sherratt’s avascular tumor growth system modeled in terms of the continuum densities of proliferating, quiescent and necrotic cells, together with the consideration of the generic nutrient supply from underlying tissue and cell movement of contact inhibition. By adopting a perturbation method combined with the Banach fixed point theorem, we theoretically justify the existence of the traveling wavefronts for this model.

The effect of amount of flour in the pre-fermented form (10%, 20%, and 30% flour in the pre-fermented form), fermentation time (12, 24, and 36 h), and amount of yeast (0.5%, 1.0%, and 1.5%) on acidity, specific volume, and crumb texture of Chinese Northern-style sourdough steamed breads were studied. Volatile compounds of the sourdough and non-sourdough steamed breads were also determined. The preferments were produced from spontaneous fermentation using all purpose (APF) and whole wheat flours (WWF). Specific volume was the highest at 20% preferment for APF sourdough steamed bread (ASSB) and 30% preferment for WWF sourdough steamed bread (WSSB). The softest texture was obtained with 20% preferment while at 30% preferment there was excessive gluten weakening due to high acidification. A total of 89 volatile compounds were identified in steamed breads with ethanol and 3-methyl-1-butanol being the most abundant compounds.

We derive a class of delay difference equations with piecewise constant nonlinearity. The convergence of solutions and the existence of asymptotically stable periodic solutions are investigated, for such a class of difference equations.

This paper is concerned with a delay differential system with piecewise constant nonlinearity. Such a differential system can be regarded as a model of two-neuron artificial neural network with delayed feedback. Some interesting results are obtained for the convergence and periodicity of solutions of the system.

In this paper, we consider a class of delay difference systems with piecewise constant nonlinearity, which includes the discrete version of an artificial neural network model of two neurons described by differential equations with piecewise constant arguments. Some interesting results are obtained for the periodicity and convergence of solutions of the systems.

This paper gives new conditions ensuring global asymptotic stability and global exponential stability for cellular neural networks with constant delay and variable delay, respectively. These conditions are derived by using the essence of piecewise linearity of the output function of cellular neural networks and by constructing Lyapunov functions and functionals. Furthermore, these conditions are significantly weaker than those given in existing literature.