Diversity of knot solitons in liquid crystals manifested by linking of preimages in torons and hopfions

Topological solitons are knots in continuous physical fields classified by non-zero Hopf index values. Despite arising in theories that span many branches of physics, from elementary particles to condensed matter and cosmology, they remain experimentally elusive and poorly understood. We introduce a method of experimental and numerical analysis of such localized structures in liquid crystals that, similar to the mathematical Hopf maps, relates all points of the medium's order parameter space to their closed-loop preimages within the three-dimensional solitons. We uncover a surprisingly large diversity of naturally occurring and laser-generated topologically nontrivial solitons with differently knotted nematic fields, which previously have not been realized in theories and experiments alike. We discuss the implications of the liquid crystal's non-polar nature on the knot soliton topology and how the medium's chirality, confinement and elastic anisotropy help to overcome the constrains of the Hobart-Derrick theorem, yielding static three-dimensional solitons without or with additional defects. Our findings will establish chiral nematics as a model system for experimental exploration of topological solitons and may impinge on understanding of such nonsingular field configurations in other branches of physics, as well as may lead to technological application

"Economics in Context: The Need for a New Textbook"

economics education, textbooks, economic theory

Chinese Porcelain and the Material Taxonomies of Medieval Rabbinic Law: Encounters with Disruptive Substances in Twelfth-Century Yemen

This article focuses on a set of legal questions about ṣīnī vessels (literally, “Chinese” vessels) sent from the Jewish community in Aden to Fustat (Old Cairo) in the mid-1130s CE and now preserved among the Cairo Geniza holdings in Cambridge University Library. This is the earliest dated and localized query about the status of ṣīnī vessels with respect to the Jewish law of vessels used for food consumption. Our analysis of these queries suggests that their phrasing and timing can be linked to the contemporaneous appearance in the Yemen of a new type of Chinese ceramic ware, qingbai, which confounded and destabilized the material taxonomies underpinning rabbinic Judaism. Marshalling evidence from contemporary Jewish legal compendia and other writings produced in this milieu, our discussion substantially advances interpretive angles first suggested by S. D. Goitein and Mordechai A. Friedman to examine the efforts of Adeni Jews to place this Chinese ceramic fabric among already legislated substances, notably the “neighboring” substances of glass and earthenware, in order to derive clear rules for the proper use and purification of vessels manufactured from it

Tuning and Switching a Plasmonic Quantum Dot Sandwich in a Nematic Line Defect

We study the quantum-mechanical effects arising in a single semiconductor core/shell quantum dot controllably sandwiched between two plasmonic nanorods. Control over the position and the sandwich confinement structure is achieved by the use of a linear-trap, liquid-crystal line defect and laser tweezers that push the sandwich together. This arrangement allows for the study of exciton plasmon interactions in a single structure, unaltered by ensemble effects or the complexity of dielectric interfaces. We demonstrate the effect of plasmonic confinement on the photon-antibunching behavior of the quantum dot and its luminescence lifetime. The quantum dot behaves as a single emitter when nanorods are far away from the quantum dot but shows possible multiexciton emission and a significantly decreased lifetime when tightly confined in a plasmonic sandwich. These findings demonstrate that liquid crystal defects, combined with laser tweezers, enable a versatile platform to study plasmonic coupling phenomena in a nanoscale laboratory, where all elements can be arranged almost at will.Comment: Supporting information at the en

More Than Mortar: Glia as Architects of Nervous System Development and Disease

Glial cells are an essential component of the nervous system of vertebrates and invertebrates. In the human brain, glia are as numerous as neurons, yet the importance of glia to nearly every aspect of nervous system development has only been expounded over the last several decades. Glia are now known to regulate neural specification, synaptogenesis, synapse function, and even broad circuit function. Given their ubiquity, it is not surprising that the contribution of glia to neuronal disease pathogenesis is a growing area of research. In this review, we will summarize the accumulated evidence of glial participation in several distinct phases of nervous system development and organization—neural specification, circuit wiring, and circuit function. Finally, we will highlight how these early developmental roles of glia contribute to nervous system dysfunction in neurodevelopmental and neurodegenerative disorder