Lattice dynamics and self-trapped excitons in the Cs2SnBr6double perovskites.

Our study delved into the detailed investigation of Cs2SnBr6double perovskites, focusing on their electrical properties, lattice dynamics, and stability. The direct bandgap for Cs2SnBr6was estimated to be at 2.93 eV. One external translational mode of the Cs+lattice withT2gsymmetry and three internal modes of the octahedral withA1g,Eg, andT2gsymmetries are defined by calculated lattice dynamics, experimental micro-Raman scattering. We show a correlation with first-principles calculations, validating using a band-structured electronic approach to understanding the behavior of charge carriers, and electron-phonon interactions in Cs2SnBr6. We propose that electron-vibration interactions result in self-trapped excitons (STEs) displaying significant Stokes shifts (0.508 eV) and broad-spectrum emission. Understanding the behavior of STEs is fundamental for their optoelectronic applications.

Sequence dependent aggregation of peptides and fibril formation.

Deciphering the links between amino acid sequence and amyloid fibril formation is key for understanding protein misfolding diseases. Here we use Monte Carlo simulations to study the aggregation of short peptides in a coarse-grained model with hydrophobic-polar (HP) amino acid sequences and correlated side chain orientations for hydrophobic contacts. A significant heterogeneity is observed in the aggregate structures and in the thermodynamics of aggregation for systems of different HP sequences and different numbers of peptides. Fibril-like ordered aggregates are found for several sequences that contain the common HPH pattern, while other sequences may form helix bundles or disordered aggregates. A wide variation of the aggregation transition temperatures among sequences, even among those of the same hydrophobic fraction, indicates that not all sequences undergo aggregation at a presumable physiological temperature. The transition is found to be the most cooperative for sequences forming fibril-like structures. For a fibril-prone sequence, it is shown that fibril formation follows the nucleation and growth mechanism. Interestingly, a binary mixture of peptides of an aggregation-prone and a non-aggregation-prone sequence shows the association and conversion of the latter to the fibrillar structure. Our study highlights the role of a sequence in selecting fibril-like aggregates and also the impact of a structural template on fibril formation by peptides of unrelated sequences.

Suppression of cardiac alternans by alternating-period-feedback stimulations.

Alternans response, comprising a sequence of alternating long and short action potential durations in heart tissue, seen during rapid periodic pacing can lead to conduction block resulting in potentially fatal cardiac failure. A method of pacing with feedback control is proposed to reduce the alternans and therefore the probability of subsequent cardiac failure. The reduction is achieved by feedback control using small perturbations of constant magnitude to the original, alternans-generating pacing period T, viz., using sequences of two alternating periods of T+ΔT and T-ΔT, with ΔT<