Discrete modulational instability and bright localized spin wave modes in easy-axis weak ferromagnetic spin chains involving the next-nearest-neighbor coupling

We report a theoretical work on the properties of modulational instability and bright type nonlinear localized modes in one-dimensional easy-axis weak ferromagnetic spin lattices involving next-nearest-neighbor couplings.With a linear stability analysis, we calculate the growth rates of the modulational instability, and plot the instability regions.When the strength of the next-nearest-neighbor coupling is large enough, two new asymmetric modulational instability regions appear near the boundary of the first Brillouin zone.Furthermore, analytical forms of the bright nonlinear localized modes are constructed by means of a quasi-discreteness approach.The influence of the next-nearest-neighbor coupling on the Brillouin zone center mode and boundary mode are discussed.In particular, we discover a reversal phenomenon of the propagation direction of the Brillouin zone boundary mode.

A stretchable and adhesive ionic conductor based on polyacrylic acid and deep eutectic solvents

Hydrogels are a widely used ionic conductor in on-skin electronic and iontronic devices.However,hydrogels dehydrate in the open air and freeze at low temperatures,limiting their real applications when they are attached on skin or exposed to low temperatures.Polymer-ionic liquid gels can overcome these two obstacles,but synthetic ionic liquids are expensive and toxic.In this work,we present an ionic conductor based on polyacrylic acid(PAAc)and deep eutectic solvents(DESs)that well addresses the aforementioned challenges.We polymerize acrylic acid in DESs to get the PAAc–DES gel,which exhibits excellent stretchability(>1000%),high electrical conductivity(1.26 mS cm^(−1)),high adhesion to the skin(~100 Nm^(−1)),as well as good anti-drying and anti-freezing properties.We also demonstrate that the PAAc-DES gel can be used as an on-skin electrode to record the surface electromyographic signal with high signal quality,or as a transparent stretchable electrode in iontronic devices that can work at–20℃.We believe that the PAAc–DES gels are an ideal candidate as epidermal electrodes or transparent stretchable electrodes.