Unlike regular elastic materials, when auxetic materials are compressed, they become thinner in the direction perpendicular to the applied force. Despite their outstanding mechanical properties, a systematic design of new and controlled auxetics remains underdeveloped. Here we establish a unified framework to describe bidimensional perfect auxetics with potential use in the design of new materials. Inspired by a natural connection between rotating rigid units and antiferromagnetic spin systems, we unveil the conditions for the emergence of a non-trivial floppy mode responsible for the auxetic behaviour. This model establishes three simple steps to design new auxetics. In particular, we constructed an exotic crystal, a Penrose quasi-crystal and the long-desired isotropic auxetic. The auxeticity of these designs is robust under small structural disturbances, as seen from experiments and numerical simulations. We expect that this work will allow the implementation of auxetic behaviour into advanced materials to enhance their functionalities, with a promising extension into 3D auxetics.
Resumenestudios previos señalan que estímulos externos asociados a drogas adquieren propiedades motivacionales que llegan a controlar la respuesta operante de búsqueda/consumo de droga y otro tipo de recompensas. la presente investigación tiene como objetivo demostrar que los eCs asociados al efecto del etanol adquieren propiedades motivacionales modificando la tasa de respuesta operante para la obtención de comida. Para ello se realizó un experimento de transferencia de control con ratas albinas. al grupo experimental se le hicieron presentaciones contingentes del eC (tono) y el estímulo incondicionado (eI) (i.e., efecto del etanol). los sujetos del grupo control tuvieron exposiciones aleatorias eC/eI. Posteriormente se comparó la tasa de respuesta operante para la búsqueda de comida frente al eC al etanol en el grupo experimental y control. los resultados indican que los eCs asociados al efecto del etanol aumentan la respuesta operante frente a reforzadores naturales.Palabras clave: condicionamiento clásico, condicionamiento operante, transferencia de control, tolerancia a las drogas.
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