Resonance phenomena in discrete systems with bichromatic input signal

We undertake a detailed numerical study of the twin phenomenon of stochastic and vibrational resonance in a discrete model system in the presence of bichromatic input signal. A two parameter cubic map is used as the model that combines the features of both bistable and threshold systems. In addition to the results already shown for continuous systems, our analysis brings out several interesting features both for vibrational and stochastic resonance, including the existence of a cross over behavior between the two. In the regime of vibrational resonance, it is shown that the additional high frequency forcing can change the effective value of the system parameter resulting in the shift of the bistable window. In the case of stochastic resonance, the study reveals a fundamental difference between the bistable and threshold mechanisms in the response, with respect to multisignal input.     

What Is the Catalytic Mechanism of Enzymatic Histone N-Methyl Arginine Demethylation and Can It Be Influenced by an External Electric Field?

Arginine methylation is an important mechanism of epigenetic regulation. Some Fe(II) and 2-oxoglutarate dependent Jumonji-C (JmjC) Nϵ-methyl lysine histone demethylases also have N-methyl arginine demethylase activity. We report combined molecular dynamic (MD) and Quantum Mechanical/Molecular Mechanical (QM/MM) studies on the mechanism of N-methyl arginine demethylation by human KDM4E and compare the results with those reported for N-methyl lysine demethylation by KDM4A. At the KDM4E active site, Glu191, Asn291, and Ser197 form a conserved scaffold that restricts substrate dynamics; substrate binding is also mediated by an out of active site hydrogen-bond between the substrate Ser1 and Tyr178. The calculations imply that in either C−H or N−H potential bond cleaving pathways for hydrogen atom transfer (HAT) during N-methyl arginine demethylation, electron transfer occurs via a σ-channel; the transition state for the N−H pathway is ∼10 kcal/mol higher than for the C−H pathway due to the higher bond dissociation energy of the N−H bond. The results of applying external electric fields (EEFs) reveal EEFs with positive field strengths parallel to the Fe=O bond have a significant barrier-lowering effect on the C−H pathway, by contrast, such EEFs inhibit the N−H activation rate. The overall results imply that KDM4 catalyzed N-methyl arginine demethylation and N-methyl lysine demethylation occur via similar C−H abstraction and rebound mechanisms leading to methyl group hydroxylation, though there are differences in the interactions leading to productive binding of intermediates.     

Oscillatory variation in EMF developed due to additions of TiO2 pretreated thermally and γ-irradiated to various doses in the concentration cell made up of Ag/Ag+

Several powder samples of TiO₂ are pretreated thermally at 300, 480 and 540°C, subjected to -irradiation and after irradiation added in one of the compartment of the concentration cell made up of Ag/Ag⁺. The adsorbed oxygen species O _2ad ^– , HO _2ad ^– and O _ad ^– on TiO₂ provide negatively charged sites and develop EMF in the cell. The radiation damage, measured in terms of equilibrium EMF, received at lower doses is partially recovered at higher doses. It is proposed that in heating at 480°C, ad species react with Ti³⁺ ions in the surface and produce –O–O– peroxy linkages and block the negatively charged sites while in heating at 540°C Ti₄O₇ phase is produced on the surface which adsorbs O₂ and provide large number of negatively charged sites. During -irradiation peroxy linkages are broken and the Ti₄O₇ phase is destroyed. Observed oscillatory variation in equilibrium EMF is explained on the basis of several reactions mentioned above proceeding at different rates during radiolysis.