1,721,113 research outputs found
Rayleigh-Lagrange formalism for classical dissipative systems
No full textIt is often believed that the Rayleigh-Lagrange formalism for classical dissipative systems is unable to encompass forces described by nonlinear functions of the velocities. Here we show that this is indeed a misconception
Variational theory for nematoacoustics
No full textThe effect of an ultrasonic wave on the nematic texture has long been known, but its interpretation in terms of a coherent dynamical theory has not yet been achieved. A proposal for such a theory is made in this paper. The diverse theoretical approaches attempted in the past to describe the interaction between sound and nematic molecular orientation are briefly summarized. A theory for second-grade fluids, which provides the appropriate theoretical background for nematoacoustics, is also revived. An explicit application of the proposed theory to a simple computable case is given, which yields predictions that are qualitatively confirmed by a number of experimental results
Chain paradoxes
No full textFor nearly two centuries, the dynamics of chains have offered examples of paradoxical theoretical predictions. Here, we propose a theory for the dissipative dynamics of one-dimensional continua with singularities which provides a unified treatment for chain problems that have suffered from paradoxical solutions. These problems are duly solved within the present theory and their paradoxes removed-we hope
Double-well elastic theory for twist-bend nematic phases
No full textThe ground state of twist-bend nematic liquid crystals is a heliconical molecular arrangement in which the
nematic director precesses uniformly about an axis, making a fixed angle with it. Both precession senses are
allowed in the ground state of these phases. When one of the two helicities is prescribed, a single helical nematic
phase emerges. A quadratic elastic theory is proposed here for each of these phases which features the same
elastic constants as the classical theory of the nematic phase, requiring all of them to be positive. To describe the
helix axis, it introduces an extra director field which becomes redundant for ordinary nematics. Putting together
helical nematics with opposite helicities, we reconstruct a twist-bend nematic, for which the quadratic elastic
energies of the two helical variants are combined in a nonconvex energy. States with minimal energy and opposite
helicities may come in contact along an interface belonging to a specia
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