Arsenopyrite weathering under conditions of simulated calcareous soil.

Mining activities release arsenopyrite into calcareous soils where it undergoes weathering generating toxic compounds. The research evaluates the environmental impacts of these processes under semi-alkaline carbonated conditions. Electrochemical (cyclic voltammetry, chronoamperometry, EIS), spectroscopic (Raman, XPS), and microscopic (SEM, AFM, TEM) techniques are combined along with chemical analyses of leachates collected from simulated arsenopyrite weathering to comprehensively examine the interfacial mechanisms. Early oxidation stages enhance mineral reactivity through the formation of surface sulfur phases (e.g., S n (2-)/S(0)) with semiconductor properties, leading to oscillatory mineral reactivity. Subsequent steps entail the generation of intermediate siderite (FeCO3)-like, followed by the formation of low-compact mass sub-micro ferric oxyhydroxides (α, γ-FeOOH) with adsorbed arsenic (mainly As(III), and lower amounts of As(V)). In addition, weathering reactions can be influenced by accessible arsenic resulting in the formation of a symplesite (Fe3(AsO4)3)-like compound which is dependent on the amount of accessible arsenic in the system. It is proposed that arsenic release occurs via diffusion across secondary α, γ-FeOOH structures during arsenopyrite weathering. We suggest weathering mechanisms of arsenopyrite in calcareous soil and environmental implications based on experimental data.

Reduction of enterotoxin induced fluid accumulation in ileal loops of neonatal calves with anti-F5 fimbriae recombinant antibody.

Neonatal calf colibacillosis caused by enterotoxigenic Escherichia coli (ETEC) is an economically significant problem in most parts of the world. The most common ETEC found in calves express the F5 (K99) fimbriae, which are necessary for the attachment of the bacteria to the ganglioside receptors on enterocytes. It is known that prevention of ETEC F5(+) adhesion to its ganglioside receptors with specific antibodies protects calves from colibacillosis. Previously we have described the development and characterization of a mouse recombinant antibody fragment (moRAb) that prevents F5 fimbrial protein induced agglutination of horse red blood cells (HRBC), which exhibit the same gangloside receptor for F5 fimbriae. Here we demonstrate that this recombinant antibody fragment inhibits in vitro the attachment of ETEC F5(+) bacteria to HRBC as well as isolated calf enterocytes, and in vivo it decreases fluid accumulation in intestinal loops of calves. Thus, correct oral administration of this anti-F5 moRAb may serve as an immunoprophylactic for cost effective control of colibacillosis in calves.

A note on the use of optimal control on a discrete time model of influenza dynamics.

A discrete time Susceptible - Asymptomatic - Infectious - Treated - Recovered (SAITR) model is introduced in the context of influenza transmission. We evaluate the potential effect of control measures such as social distancing and antiviral treatment on the dynamics of a single outbreak. Optimal control theory is applied to identify the best way of reducing morbidity and mortality at a minimal cost. The problem is solved by using a discrete version of Pontryagin's maximum principle. Numerical results show that dual strategies have stronger impact in the reduction of the final epidemic size.

Adaptive human behavior in epidemiological models.

The science and management of infectious disease are entering a new stage. Increasingly public policy to manage epidemics focuses on motivating people, through social distancing policies, to alter their behavior to reduce contacts and reduce public disease risk. Person-to-person contacts drive human disease dynamics. People value such contacts and are willing to accept some disease risk to gain contact-related benefits. The cost-benefit trade-offs that shape contact behavior, and hence the course of epidemics, are often only implicitly incorporated in epidemiological models. This approach creates difficulty in parsing out the effects of adaptive behavior. We use an epidemiological-economic model of disease dynamics to explicitly model the trade-offs that drive person-to-person contact decisions. Results indicate that including adaptive human behavior significantly changes the predicted course of epidemics and that this inclusion has implications for parameter estimation and interpretation and for the development of social distancing policies. Acknowledging adaptive behavior requires a shift in thinking about epidemiological processes and parameters.

Allosteric transition and binding of small molecule effectors causes curvature change in central ß-sheets of selected enzymes.

A quantitative description of allosteric transition remains a significant science challenge. Many allosteric enzymes contain a central ß-sheet in their catalytic domain. When an allosteric protein undergoes the transition between T (tense) and R (relaxed) allosteric states, this central ß-sheet undergoes a conformational change. A traditional method of measuring this change, the root mean square deviation (RMSD), appears to be inadequate to describe such changes in meaningful quantitative manner. We designed a novel quantitative method to demonstrate this conformational transition by measuring the change in curvature of the central ß-sheet when enzymes transition between allosteric states. The curvature was established by calculating the semiaxes of a 3-D hyperboloid fitted by least squares to the Cα atomic positions of the ß-sheet. The two enzymes selected for this study, fructose 1,6-bisphosphatase (FBPase) from pig kidney and aspartate carbamoyltransferase (ATCase) from E. coli, showed while transitioning between the allosteric states (T ⇔ R) a notable change in ß-sheet curvature (∼5%) that results in a large lateral shift at the sheet's edge, which is necessary to convey the signal. The results suggest that the ß-sheet participates in storing elastic energy associated with the transition. Establishing a tentative link between the energetics of the ß-sheet in different allosteric states provides a more objective basis for the naming convention of allosteric states (tense or relaxed), and provides insight into the hysteretic nature of the transition. The approach presented here allows for a better understanding of the internal dynamics of allosteric enzymes by defining the domains that directly participate in the transition.