Exciton swapping in a twisted graphene bilayer as a solid-state realization of a two-brane model

It is shown that exciton swapping between two graphene sheets may occur under specific conditions. A magnetically tunable optical filter is described to demonstrate this new effect. Mathematically, it is shown that two turbostratic graphene layers can be described as a "noncommutative" two-sheeted (2+1)-spacetime thanks to a formalism previously introduced for the study of braneworlds in high energy physics. The Hamiltonian of the model contains a coupling term connecting the two layers which is similar to the coupling existing between two braneworlds at a quantum level. In the present case, this term is related to a K-K' intervalley coupling. In addition, the experimental observation of this effect could be a way to assess the relevance of some theoretical concepts of the braneworld hypothesis.Comment: 15 pages, 3 figures, final version published in European Physical Journal

NEOTROPICAL XENARTHRANS: a data set of occurrence of xenarthran species in the Neotropics

Xenarthrans – anteaters, sloths, and armadillos – have essential functions for ecosystem maintenance, such as insect control and nutrient cycling, playing key roles as ecosystem engineers. Because of habitat loss and fragmentation, hunting pressure, and conflicts with 24 domestic dogs, these species have been threatened locally, regionally, or even across their full distribution ranges. The Neotropics harbor 21 species of armadillos, ten anteaters, and six sloths. Our dataset includes the families Chlamyphoridae (13), Dasypodidae (7), Myrmecophagidae (3), Bradypodidae (4), and Megalonychidae (2). We have no occurrence data on Dasypus pilosus (Dasypodidae). Regarding Cyclopedidae, until recently, only one species was recognized, but new genetic studies have revealed that the group is represented by seven species. In this data-paper, we compiled a total of 42,528 records of 31 species, represented by occurrence and quantitative data, totaling 24,847 unique georeferenced records. The geographic range is from the south of the USA, Mexico, and Caribbean countries at the northern portion of the Neotropics, to its austral distribution in Argentina, Paraguay, Chile, and Uruguay. Regarding anteaters, Myrmecophaga tridactyla has the most records (n=5,941), and Cyclopes sp. has the fewest (n=240). The armadillo species with the most data is Dasypus novemcinctus (n=11,588), and the least recorded for Calyptophractus retusus (n=33). With regards to sloth species, Bradypus variegatus has the most records (n=962), and Bradypus pygmaeus has the fewest (n=12). Our main objective with Neotropical Xenarthrans is to make occurrence and quantitative data available to facilitate more ecological research, particularly if we integrate the xenarthran data with other datasets of Neotropical Series which will become available very soon (i.e. Neotropical Carnivores, Neotropical Invasive Mammals, and Neotropical Hunters and Dogs). Therefore, studies on trophic cascades, hunting pressure, habitat loss, fragmentation effects, species invasion, and climate change effects will be possible with the Neotropical Xenarthrans dataset

Avaliação da toxicidade das favas de Stryphnodendron fissuratum (Mimosoideae) em vacas gestantes

Com o objetivo de avaliar a toxicidade de diferentes concentrações das favas de Stryphnodendron fissuratum em vacas prenhes, as favas desta árvore foram moídas, misturadas à ração comercial e fornecidas a oito vacas nas doses totais de 6,5g/kg, 7,5g/kg, 9g/kg e 10g/kg. Os animais que receberam doses de 6,5g/kg pariram bezerros normais e aqueles que receberam 7,5g/kg pariram bezerros fracos que não sobreviveram. Doses de 9g/kg resultaram no nascimento de um bezerro imaturo e de outro bezerro com distiquíase, opacidade congênita das córneas e microftalmia. Ambas as vacas que ingeriram 10g/kg morreram, porém uma vaca abortou antes de morrer. Nas vacas que morreram, as lesões macroscópicas e histológicas do sistema digestivo e fígado foram semelhantes às descritas anteriormente na intoxicação por S. fissuratum. Nos bezerros e no feto abortado não foram observadas lesões macroscópicas ou histológicas significantes. A análise fitoquímica dos extratos metanólicos das favas de S. fissuratum revelou a presença de taninos hidrossolúveis, proantocianidinas, leucoantocianidinas e da saponina triterpénica β-amirina. Saponinas triterpénicas têm sido associadas com a toxicidade das favas de Stryphnodendron spp. e Enterolobium spp., que causam sinais clínicos semelhantes aos observados na intoxicação por S. fissuratum. Esta pesquisa confirmou a toxicidade das favas de S. fissuratum para bovinos, no entanto não foram confirmados os efeitos abortivos das mesmas, pois o aborto e as mortes neonatais observadas podem ser decorrentes dos efeitos tóxicos da planta nas mães. Novas pesquisas são necessárias para pesquisar se as favas da planta causam malformações semelhantes às observas em um dos bezerros nascidos vivos