Intelligent skinlike materials have recently attracted tremendous research interests for employing in electronic skin, soft robotics, and wearable devices. Because the traditional soft matters are restricted in unsatisfactory mechanical performances or short-term usage, these materials are adverse to practical applications. Here, intriguing conductive hydrogel materials with multifunctionality (MFHs) are fabricated by using poly­(acrylic acid) (PAA), dopamine-functionalized hyaluronic acid (DHA), and Fe3+ as ionic cross-linker. The mussel-inspired networks with delicate combination of physical and chemical cross-linking possess synergistic features of inherent viscoelasticity, high stretchability (800%), and durable self-adhesiveness to various substrates. Owing to the abundant hydrogen bonds and multiple metal coordination interactions between Fe3+, catechol, and carboxylic groups, the matrix reveals repeatable thermoplasticity and autonomous self-healing property both mechanically and electrically (98% recovery in 2 s). When served as strain sensors, the MFHs can distinctly perceive complex body motions from tiny physiological signal (breathing) to large movements (knee bending) as human motion detecting devices. Moreover, the MFHs were explored as ideal material for circuit repairing, programming, and switches constructing because of their excellent properties. Consequently, these eco-friendly hydrogel ionotronic devices can be promising candidates for next-generation intelligent wearable devices and human–machine interfaces.

In this work, we prove a previously published conjecture that a prescription we gave for constructing states that implement Gauss's law for 'pure glue' QCD is correct. We also construct a unitary transformation that extends this prescription so that it produces additional states that implement Gauss's law for QCD with quarks as well as gluons. Furthermore, we use the mathematical apparatus developed in the course of this work to construct gauge-invariant spinor (quark) and gauge (gluon) field operators. We adapt this SU (3) construction for the SU (2) Yang-Mills case, and we consider the dynamical implications of these developments.

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We use a unitary operator constructed in earlier work to transform the Hamiltonian for QCD in the temporal ($A_0=0$) gauge into a representation in which the quark field is gauge-invariant, and its elementary excitations -- quark and antiquark creation and annihilation operators -- implement Gauss's law. In that representation, the interactions between gauge-dependent parts of the gauge field and the spinor (quark) field have been transformed away and replaced by long-range non-local interactions of quark color charge densities. These long-range interactions connect SU(3) color charge densities through an infinite chain of gauge-invariant gauge fields either to other SU(3) color charge densities, or to a gluon "anchor". We discuss possible implications of this formalism for low-energy processes, including confinement of quarks that are not in color singlet configurations.Comment: 9 pages, LaTeX, uses REVTe

We construct a transformation that transforms perturbative states into states that implement Gauss's law for `pure gluonic' Yang-Mills theory and QCD. The fact that this transformation is not and cannot be unitary has special significance. Previous work has shown that only states that are unitarily equivalent to perturbative states necessarily give the same S-matrix elements as are obtained with Feynman rules.Comment: 11 page

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We examine a nonlocal interaction that results from expressing the QCD Hamiltonian entirely in terms of gauge-invariant quark and gluon fields. The interaction couples one quark color-charge density to another, much as electric charge densities are coupled to each other by the Coulomb interaction in QED. In QCD, this nonlocal interaction also couples quark color-charge densities to gluonic color. We show how the leading part of the interaction between quark color-charge densities vanishes when the participating quarks are in a color singlet configuration, and that, for singlet configurations, the residual interaction weakens as the size of a packet of quarks shrinks. Because of this effect, color-singlet packets of quarks should experience final state interactions that increase in strength as these packets expand in size. For the case of an SU(2) model of QCD based on the ansatz that the gauge-invariant gauge field is a hedgehog configuration, we show how the infinite series that represents the nonlocal interaction between quark color-charge densities can be evaluated nonperturbatively, without expanding it termby-term. We discuss the implications of this model for QCD with SU(3) color and a gauge-invariant gauge field determined by QCD dynamics. *

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